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PRACTICAL ASSAYING. 



LONDON: PRINTED lil 

6P01TIS WOODS AND CO., N EW-STREET SQUARE 
AND PARLIAMENT STREET 








A MANUAL 

OF 


PRACTICAL ASSAYING. 


JOHN MITCHELL, F.C.S. 

ii ' 


THIRD EDITIOU 


EDITED DY 


WILLIAM C1100KES, F.E.S. 

I 



J). VAN N 0 S T R A N D, 

23 MURRAY STREET, 

NEW YORK. 

1872. 







PREFACE 


TO 

THE THIRD EDITION. 


The rapid progress of Science renders a metallurgical 
work antiquated in a comparatively short period, so that 
the last (second) edition of the late Mr. Mitchell’s 4 Manual 
of Practical Assaying,’ published in 1854, is no longer in 
accordance with our enlarged knowledge of the subject. 

In this edition are incorporated all the late important 
discoveries in Assaying made in this country and abroad, 
and special care is devoted to the very important Volumetric 
and Colorimetric Assays, as well as to the Blowpipe Assays. 
Most of the chapters are entirely re-written, whilst the 
chapter on Crystallography—being a subject only remotely 
bearing on Assaying — is left out altogether. On the 
other hand, in some cases, it may seem that by treating 
of purely analytical details the limits of Assaying have 
been exceeded. But these departments are so closely 
related as to make it impossible to fix the line of demar¬ 
cation between them. Moreover, chemistry is cultivated by 
almost all to whom this work is of interest or service, so 
that it is hoped these amplifications will add to its value. 



VI 


PREFACE TO THE THIRD EDITION. 


The old equivalents are retained, as they are more generally 
understood by students of science who do not make 
chemistry their chief study. 

The Editor is under many obligations to his friend Dr. 
Rohrig, M.E., for assistance in revising the manuscript 
and incorporating into the work the latest continental im¬ 
provements, as set forth in Professor Kerbs Probirkunst, 
The author of the best work on volumetric analysis which 
has yet appeared in English, Mr. Sutton, F.C.S., has kindly 
placed several cuts, &c., at the Editor’s disposal, and some 
descriptions of German processes have been taken from the 
last English Edition of Fresenius’s Quantitative Analysis —a 
work which should be a standard of reference for all students 
who desire to carry their chemical researches further than 
is possible to be treated of in a work professing to deal 
only with Assaying. 


London : September, 1868. 


PREFACE 


TO 

THE SECOND EDITION. 


In presenting this the Second Edition of the ‘ Manual of 
Practical Assaying ’ to his mining friends and the public in 
general, the author has to tender his sincere thanks for the 
very favourable opinion expressed of the former edition, 
which was honoured with a most extensive circulation, not 
only in the United Kingdom, but in all the Colonies, the 
United States, and South America: in addition to which it 
was translated into Spanish, for the use of the Government 
School of Mines at Madrid. 

The former edition having been out of print for some 
time, repeated calls have been made on the author for a 
Second Edition; and, in compliance with this general re¬ 
quest, the present volume has been prepared. The same 
arrangement (as far as practicable) has been adhered to as 
in the first edition, but a considerable portion has been 
entirely re-written, and much new matter added. It is also 
embellished with nearly 400 engravings illustrative of 
crystallography, and the various apparatus described in the 
body of the work. 




PREFACE TO 


• • • 

Vlll 

In its preparation, the author lias been greatly influenced 
by a desire to extend the sphere of utility of the former 
edition, by introducing, in the smallest possible space, and 
in the simplest form, such instructions in elementary 
chemistry, chemical notation, the use of chemical symbols, 
&c. as will enable the assayer or metallurgist to trace the 
varied re-actions occurring either in the crucible or the 
furnace during the progress of an experiment. 

Crystallography has also been made the subject of attention 
with a view to the discrimination of mineral substances by 
crystalline forms, aided by a few chemical tests. 

Under the assay of Silver, there is added a full and com¬ 
plete description of the mode of assay employed in the 
Paris Mint, together with engravings of the apparatus in 
use. 

A chapter has also been introduced, containing full in¬ 
structions for the discrimination of all the more commonly 
occurring Gems and Precious Stones ; and in the Appendix 
will be found copious Tables for the Valuation of Gold of 
every degree of fineness, expressed either in carats or thou¬ 
sandths ; following which is an Assay Table, for calculating 
the number of ounces, pennyweights, and grains of gold or 
silver in a ton of mineral, when a given quantity has been 
submitted to assay. 


In conclusion, the astounding discoveries of mineral 
wealth which are now daily being made, not only in this 
country, but in every other to which a due amount of 
diligence and information has been turned, renders the 
appearance of a complete Manual of the more closely 


THE SECOND EDITION. 


IX 


allied branches of knowledge involved in the successful 
cultivation of such researches a desideratum of considerable 
importance. 

The present volume, it is hoped, will fill the existing void 
in the literature subservient to this branch of our know¬ 
ledge. 


Assay Office, 

Dunning’s Alley, Bishopsgate Street Without. 

















































































* 

' ii 

' 





















PREFACE 


TO 

THE FIRST EDITION. 


When the rank our country holds among nations, as regards 
her Mining interest, is taken into consideration, it must be 
with all a matter of surprise that no work especially devoted 
to the elucidation of the processes to be employed in ascer¬ 
taining the richness in metal of any sample of ore (that is, 
in other terms, its Assay) has of late years appeared before 
t he British public. Indeed, the only work at present known 
in England is Berthicr’s c Traite des Essais par la Voie 
Seche,’ which, for the mere purpose of inculcating the prin¬ 
ciples of assaying, has many disadvantages—not the least 
of which is its being written in a foreign tongue ; and 
although a knowledge of French is now so very general 
yet many are prevented buying scientific works in that 
language on account of the difficulties of finding equivalents 
for the technicalities which must necessarily be employed. 
It is also a very large work, and one containing much 
matter which the assayer does not need—matter relat¬ 
ing to the composition of wood and coal ashes, furnace 
products, &c. which arc more especially adapted for the 
metallurgist. 




FREFACE TO 


Xll 


These considerations, coupled with the paucity of any 
knowledge of assaying, excepting that confined to a very 
limited number of persons, induced the author of the follow¬ 
ing pages to turn a considerable amount of his attention to 
this subject, more especially as much difficulty was ex¬ 
perienced in not having a suitable text-book for the use of 
his pupils. A portion of the following pages was drawn up 
as a Manual for such a purpose ; but on consideration, it 
was thought the extension of such a work was so much 
needed that it was determined to alter the original plan as 
far as was consistent with the complete carrying out of the 
object in view, viz. the production of a Manual embodying 
information in every branch of assaying, either by the wet 
or the dry processes. 

The following is a sketch of the manner in which this is 
accomplished; the author having followed the excellent 
arrangement of Berthier as closely as possible, from whose 
work also much matter that suited these pages, and which it 
would have been useless to re-write, has been inserted. 
Firstly, the Mechanical and Chemical Operations of Assaying 
are treated in full, inclusive of a description of the apparatus 
required, their mode of use, &c. Secondly, Furnaces, Fuel, 
and Crucibles, together with a description of the best 
Pyrometers, and their applications. Thirdly, the FJuxes, 
their properties, preparation, use, &c. Fourthly, an Essay 
on the use of the Blowpipe, and all its appurtenances; as 
Fluxes, Supports, &c. Fifthly, the action of the Fluxes on 
some Mineral Substances. Sixthly, a method of discrimina¬ 
ting many Minerals by means of the Blowpipe, aided by 
a few tests by the humid method. Seventhly, the Humid 
Analysis of many Mineral Substances, their composition, 
locality, &c. (All the minerals mentioned in the three last 
heads comprehend such only as generally come under the 


THE FIRST EDITION. 


• « • 
Xlll 

notice of the Assayer.) Eighthly, the complete Assay of all 
the common Metals, in addition to which the Assay of 
Sulphur, Chromium, Arsenic, Heating power of Fuel, &c. is 
fully discussed ; and ninthly, and lastly, a copious Table 
drawn up for the purpose of ascertaining in Assays of Gold 
and Silver the precise amount, in ounces, pennyweights, and 
grains, of Noble metal contained in a Ton of Ore from the 
assay of a given quantity. This Table is the most complete 
and copious yet published. 

Not only has it been endeavoured to collect all that is 
generally known on the subject of Assaying, but many new 
facts have been added, and such matter entered into, that 
the success of an assay is rendered much more certain ; and 
most assays are conducted more rapidly and with greater 
exactitude than heretofore. 

It has also been endeavoured to introduce a new system, 
in which is pointed out the rationale of each process, with 
the chemical action taking place between the fluxes and the 
ores in course of assay, so that by paying a careful attention 
to the matters discussed, so much of the chemical nature of 
all ores that can come under the assayer’s hand may be 
known, that the practice by ‘ rule of thumb ’ (a rule on 
which very little dependence is to be placed, excepting after 
years of the most laborious practice, and a rule which 
cannot be imparted, excepting the pupil pursue the same 
unprofitable course) must, it is hoped, be speedily abandoned 
when, by knowing the chemical properties of the body 
operated on, the necessary fluxes and processes might be 
at once indicated, and with a certainty of perfect success. 

Having premised thus much, the author must beg to ex¬ 
press his thanks to his friend Mr. F. Field for the kind 


XIV 


PREFACE TO THE FIRST EDITIOxX. 


assistance he afforded him whilst experimenting on the 
various modes of assay described in the body of the work ; 
and trusting that any little imperfections which may be 
detected will not be harshly criticised, but that it may be 
taken into consideration that the author has attempted to 
improve a branch of mining knowledge to which unfor¬ 
tunately too little attention has been devoted, and to which, 
if he has added anything useful, he is indebted for the first 
principles of such knowledge to Berthier’s 6 Traite des 
Essais,’ for which, to the talented writer of the above 
work, he is under the most lasting obligation. 


2-3 Hawley Load, Kentish Town, London. 




CONTENTS. 


CHAPTER I. 

PAGE 

Chemical nomenclature ...... i 

Non-metallic elements or metalloids, 0. Metallic elements, 3. 

Oxides ........ 4 

Salts ........ 4 

Binary compounds containing no oxygen . . .5 

Laws of combination ...... 5 

Chemical symbols ...... 7 


CHAPTER II. 


Preparation of the sample ...... 

The anvil and stand, 11. Hammers, 12. Cold chisel, 13. 
Shears, 13. The pestle and mortar, 13. Steel mortar, 16. 
Sieves, 17. 

Elutriation ....... 

Washing, dressing, or vanning . 

The balance ....... 

Three kinds of balance, 23. Conditions for accuracy of ba¬ 
lance, 25. Conditions for delicacy of balance, 27. The 
weights, 30. Assay weights for silver, 31. Assay weights 
for gold, 31. 

The method of weighing ...... 

O CJ 

Mene’s mode of weighing, 35. Mayer’s application, 35. 


9 


18 

19 

23 


32 


CHAPTER III. 


General preparatory chemical operations 

Calcination ....... 

Roasting ........ 

Roasting in tests, 10. Roasting in crucibles, 40. Roasting in 
platinum capsules, 42. 

cl 


38 

38 

40 









XVI 


CONTENTS. 


Reduction ...••••• 

Fusion . • • • • • • 

Solution ..•••••• 

Distillation ....... 

Liquid distillation, 4G. Dry distillation, 47. The pneumatic 
trough, 48. Correction for temperature, 49. Correction for 
pressure, 50. Correction for moisture, 50. 

Sublimation ....... 

Scorification : cupellation ...... 


rAOK 

42 

44 

45 

46 


51 

51 


CHAPTER IV. 


Production and application of heat . . . . .52 

Furnaces . . • • • • * .52 

Calcining furnaces . . • • • • .52 

The ashpit, 53. Chimney, 53. The body of the furnace, 53. 
Evaporating furnaces . . • • • .54 

The hood . . . . • • .54 

Fusion furnaces: wind furnaces . . . . .55 

The ashpit, 55. The bars, 56. Chimney, 56. 

Blast furnaces . . . . . . .57 

Sefstrom’s blast furnace, 58. St.-Claire Deville’s furnace, 59. 

Muffle, or cupel furnaces . . . . . .59 

Aufrye and d’Arcet’s furnaces, 60. 

Furnace operations . . . . . .63 

Auxiliary apparatus . . . . . .64 

Pokers, or stirring rods, 64. Tongs, 64. Ingot moulds, 66. 

Ladles, 66. 

Fuel for furnaces . . . . . . .66 

The effects produced by wind and blast furnaces . . .69 

Oil furnaces . . . . . . .71 


Description of the apparatus, 71. Management of the oil-lamp 
furnace, 73. Power of the oil-lamp furnace, 76. Requisite 
blowing power, 76. 

Gas blast furnace . . . . . . .77 

Gas furnace arranged for heating at the top, 80. The process 
of fusion, 82. Precautions to be observed on commencing a 
fusion, 83. Results, 84. Gas furnace heated at the bottom, 

84. Examples of fusion effected by the blast gas furnace, 

86. Fusion of metals in large quantities, and ignition of 
objects of large size, 88. Muffle furnace for assaying, roast¬ 
ing, Ac., 88. Miscellaneous use of the gas furnace, 89. 
Repair of the gas furnace, 89. ■ Griffin’s miniature gas blast 
furnace, 90. Gore’s gas furnace, 91. Griffin’s gas reverbe¬ 
ratory furnace, 96. Mounts for crucibles, 105. Supporting 
the crucibles, 106. 





XV11 


CONTEXTS. 


Lutes and cements ....... 

Fat lute, 108. Roman cement, 108. Plaster of Paris, 108. 
Linseed, or almond meal, 108. Lime and egg lute, 108. 
White lead mixed with oil, 108. Yellow wax, 108. Soft 
cement, 108. Waterproof cement, 108. Resinous, or hard 
cement, 110. Paper, 110. Bladders, 110. Caoutchouc, 
110. Faraday’s directions for luting glass or earthenware 
retorts, 111. Iron cement, 112. Beale’s cement, 113. 
Boiler cement, 113. Bruyere’s cement, 113. Oxychlo.ide 
of zinc cement, 113. 

Crucibles ........ 

London pots, 113. Cornish crucibles, 113. Hessian crucibles, 

113. Crucibles of the Patent Plumbago Crucible Company, 

114. Stourbridge crucibles, 114. Porcelain crucibles, 114. 
Black-lead crucibles, 116. Charcoal crucibles, 118. Lime 
crucibles, 121. Mr. David Forbes’s experiments on crucibles, 
121. Alumina crucibles, 122. Malleable iron Crucibles, 
123. Platinum crucibles, 123. Fresenius's directions for 
the preservation of platinum crucibles, 124. 

Cupels ........ 

The mould for making cupels, 120. 

Scorifiers ........ 

Methods of measuring the heat of furnaces . 

Wedgwood’s pyrometer, 131. Daniell's p}'rometer, 131. 
Wilson’s pyrometer, 134. Bystrbm’s pyrometer, called 
hydro-pyrometer, 134. Becquerel’s thermo-electric pyro¬ 
meter, 136. Plan for comparing the temperatures of two 
furnaces, 136. 


CHAPTER Y. 


Fuel, its assay and analysis . 

External appearance of the fuel, its porosity, compactness, fracture, 
size, and shape of pieces ...... 

Determination of the adhering water . 

Determination of the specific gravity . . . . 

Determination of the absolute heating power 

Pyrometric heating power, 141. Different methods of ascer¬ 
taining the absolute heating power, 141. Berthier's method, 
141. Ure’s method, 144. lire’s calorimeter, 147. 
Determination of the specific heating power 
Determination of the pyrometric heating power 
Determination of the volatile products of carbonisation 
Examination of the coke or charcoal left behind on carbonisation . 
Determination of the amount of ash » 

Determination of the amount of sulphur . 

Examination of other peculiarities of fuel , 


PAGE 

107 


113 


128 

130 

131 


138 

139 

140 

140 

141 


148 

148 

149 

150 

150 

151 

152 






XV111 


CONTEXTS, 


CHAPTER VI. 


Reducing agents ....... 

Hydrogen gas, 154. Carbon, 155. Black-lead or graphite, 
155. Anthracite, 155. Coke, 155. Wood charcoal, 155. The 
fat oils, 157. Tallow, 157. Resins, 157. Sugar, 157. Starch, 
158. Gum, 158. Tartaric acid, 158. Oxalic acid, 158. 
Oxalate of ammonia, 159. Comparative reducing power of 
the above agents, 159. Metallic iron, 159. Metallic lead, 
160. 

Oxidising agents ....... 

Oxygen, 1G0. Litharge, 1G0. Ceruse, or white lead, 1G1. 
Action of oxide of lead on the following metals and metal¬ 
loids:—Sulphur, 1G1. Selenium, 161. Tellurium, 161. 
Arsenic, 161. Antimony, 162. Tin, 163. Zinc, 163. 
Bismuth, 163. Iron, 164. Copper, 164. 

Action of the oxides of copper upon lead, 165. Silicates and 
borate of lead, 166. 

Nitrates of potash and soda, 166. Different modes of assaying 
saltpetre, 167. Huss’s mode, 167. Gay-Lussac’s mode, 
169. Foreign substances in raw saltpetre, 169. Assay of 
gunpowder, 172. 

Nitrates of lead, 173. Peroxide of manganese, 173. Oxide 
of copper, 173. Peroxide of iron, 173. The caustic alka¬ 
lies, potash and soda, 173. Carbonate of potash and soda, 

173. Sulphates of lead, copper and iron, 173. Sulphate 
of soda, 174. 

Desulphurising reagents ...... 

The oxygen of the atmosphere, 174. Charcoal, 175. Iron, 

174. 

Litharge, 174. Its behaviour with the following sulphides: 
—Sulphide of manganese, 175. Sulphide of iron, 176. 
Sulphide of copper, 177. Sulphide of antimony, 178. 
Sulphide of zinc, 179. Sulphide of lead, 179. 

Caustic alkalies and their carbonate, 180. Nitre, saltpetre, or 
nitrate of potash, 181. Nitrate of lead, 181. Sulphate of 
lead, 181. 

Sulphurising reagents . .... 

Sulphur, 181. Cinnabar, 182. Galena, 182. Sulphide of 
antimony, 182. Iron pyrites, 182. Alkaline persulphides, 
182. 

Fluxes ........ 

Non-metallic fluxes ..... 

• • 

Silica, 18 4. Lime, magnesia, alumina, and their silicates, 185. 
Glass, 185. Analysis of different kinds of glass, 186. 

Borax, 185. Fluor spar, 187. Carbonate of potash and 
carbonate of soda, 187. Nitrate of potash, 188. Common 


PAGE 

154 


160 


174 


181 


183 

184 



CONTEXTS. 


XIX 


PAGE 

salt or chloride of sodium, 188. Black flux, white flux, and 
raw flux, 189. Argol, cream of tartar, or bitartrate of potash, 

191. Salt of sorrel, or binoxalate of potash, 191. White 
and mottled soap, 192. 

Metallic fluxes ....... 193 

Litharge and ceruse, 193. Glass of lead, 193. Borate of lead, 

193. Sulphate of lead, 193. Oxide of copper, 194. The 
oxides of iron, 194. 


CHAPTER VII. 


The blowpipe and its use . . . . . .195 

The blowpipe, 196. Flame for the blowpipe, 198. Faraday’s 
directions for using the blowpipe, 199. Oxidation, 202. Re¬ 
duction, 202. 

Auxiliary blowpipe apparatus, &c. :—Supports, 202. Charcoal, 

203. Platinum, 204. 

Fluxes and reagents, 205. 

Reagents in the humid way . . . . .205 

Reagents used as simple solvents ..... 205 

Distilled water, 205. Alcohol, 205. Ether, 205. 

Reagents principally employed as chemical solvents . . 205 

Hydrochloric acid, 205. Nitric acid, 205. Nitro-hydro- 
chloric acid, 205. Acetic acid, 205. Chloride of ammo¬ 
nium, 205. 

Reagents used to separate, or otherwise characterise, groups of sub- 

* stances ....... 206 

Reagent papers (blue litmus paper, reddened litmus paper, 
brazilwood paper, turmeric paper), 206. Sulphuric acid, 

206. Sulphuretted hydrogen, 206. Sulphide of ammonium, 

206. Solution of potash, 206. Ammonia, 206. Carbonate 
of ammonia, 206. Chloride of barium, 206. Nitrate of 
baryta, 206. Chloride of calcium, 207. Sesquicliloride of 
iron, 207. 

Reagents used for the detection of bases .... 207 

Sulphate of potash, 207. Chromate of potash, 207. Cyanide of 
potassium, 207. Ferrocyanide of potassium, 207. Ferrid- 
cyanideof potassium, 207. Sulpliocyanide of potassium, 208. 
Phosphate of soda, 208. Oxalate of ammonia, 208. Proto¬ 
chloride of tin, 208. Bichloride of Platinum, 209. Perehloride 
of gold, 209. Zinc, 209. Copper, 209. Ron wire, 209. 

Special reagents employed for determining the presence of acids . 209 

Acetate of potash, 209. Hydrate of lime, lime-water, 209. 
Sulphate of lime, 209. Sulphate of magnesia, 209. Chlo¬ 
ride of magnesium, 210. Sulphate of iron, 210. Neutral 


4 


XX 


CONTEXTS. 


PAOE 

acetate of lead, 210. Sulphate of copper, 213. Subnitrate 
of mercury, 210. Oxide of mercury, 210. Chloride of 
mercury, 210. Sulphurous acid, 210. Chlorine, 210. Sulph- 
indigotic acid, 210, Starch paste, 210. 

Ileagents in the dry way . . . . . .210 

Carbonate of soda, 210. The fusion of substances with soda, 

210. Reduction of metallic oxides, 212. 

Borax, 214. Ammonio-phosphate of soda or microcosmic salt, 

215. Nitrate of potash or nitre, 21G. Bisulphate of potash, 

217. Vitrified boracic acid, 218. Nitrate of cobalt, 218. 
Oxalate of nickel, 218. Oxide of copper, 218. Silica, 218. 
Fluoride of calcium (fluorspar), and sulphate of lime 
(gypsum), 218. Bone ashes, 219. Proof lead, 219. Tinfoil, 

219. Dry chloride of silver (Guericke’s proposal), 219. 


General routine of blowpipe operations .... 224 

Size of the assay, 224. Soda paper, 224. 

Rose’s list of minerals of different degrees of fusibility . . 22G 

The employment of fluxes ...... 227 

Blowpipe reactions....... 228 


Potash, soda, and lithia, 228. Baryta, 228. Strontia, 229. 

Lime, 229. Magnesia, 229. Alumina, 229. Molybdic 
acid, 230. Tungstic acid, 230. Silica, 231. Sulphur, 231. 
Sulphides, 231. Selenium and selenides, 232. Sulphates, 232. 
Nitrates, 233. Bromides, 233. Iodides, 233. Chlorides, 

233. Fluorides, 233. Phosphates, 234. Hydrates, 234. 
Silicates, 234. 

Coloured flames . . . . . . .234 

Blue flames, 235. Green flames, 235. Yellow flames, 235. 

Red flames, 235. Chlorine, 235. Lead, 23G. Arsenic, 

23G. Selenium and Arsenic, 23G. Bromine, 23G. Boracic 
acid, 23G. Tellurium, 236. Copper, 236. Iodine and 
Copper, 23G. Phosphoric acid, 237. Baryta, 237. Zinc, 

237. Soda, 237. Water, 237. Strontia, 237. Lithia, 237. 

Lime, 237. Potash, 237. 


CHAPTER VIII. 

Volumetric analysis ••.... 238 

The reactions of volumetric analysis, 238. The principle of 
it, 238. Standard solutions, 245. 

The instruments and apparatus, 246. The burette, 246. The 
pipette, 249. The measuring flasks, 249. 

Colorimetric analysis 


250 


CONTEXTS. 


XXI 


CHAPTER IX. 

PAGE 

The assay of Iron . . . . . . .251 

The ores of Iron ....... 251 

Magnetic Iron ore, 251. Red haematite, 251. Brown haema¬ 
tite, 251. Spathic carbonate, 251. Argillaceous Iron ore, 

251. Blackband, 252. Red siliceous Iron, 252. 

The assay of Iron in the dry way ..... 252 

Classification of the Iron ores, 252. Fluxes, 253. Air-furnaces, 

254. Crucibles, 254. Assay-operation, 255. Results, 255. 
Berthier’s method for estimating the other, chiefly slag¬ 
forming, components of the Iron ores, 25G. 

Professor Abel’s process for the complete assay of Iron and Iron 
ores ........ 259 

Analyses of the Iron samples, 263. Preparation of the sample, 

263. Chemical analysis, 263. Sulphur, 264. Carbon as 
graphite, 264. Silicon, 264. Manganese, 265. Phosphorus, 

265. Combined carbon, 266. Minute proportions of foreign 
metals, 266. 

Analysis of Iron ores, 267. Analysis of the samples of fluxes, 

267. 

The assay of Iron in the wet way . . . . .268 

Fuchs’s method . . . . . . .268 

Marguerite’s process . . . . . .269 

Various operations of the process, 270. Fresenius’ observations 
on the determination of Iron in hydrochloric acid solution by 
this process, 273. Blunt’s observations on the process, 274. 

Dr. Penny’s process . . . . . .275 

Mittenzwey’s process . . . . . .281 

Titration of Iron by protochloride of tin . . . .282 

Quantitative determination of all the constituents usually present in 
an Iron ore . . . . . . .286 

Determination of silica, oxide of iron, and oxide of manganese, 

286. Determination of lime, magnesia, and part of phos¬ 
phoric acid, 288. Treatment of the precipitate, 288. Treat¬ 
ment of the alkaline solution poured off from the first black 
precipitate ; determination of alumina and remainder of phos¬ 
phoric acid, 289. Determination of potash and soda, 290. 
Determination of sulphur, 291. Determination of carbonic 
acid, 291. Determination of water, 293. 

Blowpipe reactions of Iron ores . . . . .293 

Sulphide of Iron (magnetic pyrites), 293. Common pyrites, 

293. Mispickel (arsenical pyrites), 293. Magnetic Iron 
ore and oxide of Iron, 294. Carbonate of oxide of Iron, 

294. Chromate of Iron, 294. Hydrated oxide of Iron, 294. 
Oxides of Iron, 294. Chapman’s method for distinguishing 
protoxide of Iron from sesquioxide, 295. 


xx ii 


CONTEXTS. 


CHAPTER X. 


The assay of Copper ...... 

Classification of minerals and substances containing Copper 

Class I. Sulphuretted ores or products with or without sele¬ 
nium, antimony, or arsenic :—Copper glance, 207. Chalco- 
rite, 297. Erubesoite, 207. Bournonite, 297. Fahlerz, 
297. Covelline, 297. Wollsbergite, 297. Domeykitc, 297. 
Copper regulus, speiss, 297. 

Class II. Oxidised ores and products:—Red Copper, 297. 
Malachite, 297. Azurite, 297. Cyanosite, 297. Phos¬ 
phate of Copper, 297. Arseniate of Copper, 297. Chromate, 
vanadate, and silicate of Copper, slags, &c., 297. 

Class III. Copper and its alloys. 

Classification of the different methods of assaying Copper 

A. Assay in the dry way ..... 

a. For rich ores and products of Class I. 

English Copper assay ..... 

Moissenet’s description, 299. Ticketing in Cornwall, 
299. Division adopted, 300. 

Sect. I. Reactions, 301. 

Two kinds of assays, viz. the roasted sample and 
the raw sample, 301. 

1. Regulus, 302. 

Pyrites, 302. Very poor pyrites, 302. 
Variegated Copper ore, 303. Sulphide 
of Copper, 303. Carbonated minerals, 
303. Native mixture, 303. 

2. Calcining, 304. 

3. Coarse Copper, 304. 

4. Washings, 305. 

5. Testing, refining, 300. 

0. Slags for prill, 307. 

Sect. II. Manipulations, 307 :— 

Crucibles used in Cornwall; 308. Furnace, 308. 
Fusion for regulus, 309. Calcining the regulus 
(matt), 312. Fusion for coarse Copper, 313. 
One or two fusions with fluxes (washings), 314. 
Testing and refining, 314. Treatment of slags 
for prill, 314. 

Sect. III. Some minerals and substances of a special 
nature. Influence of foreign metals :— 
Stanniferous minerals, 315. Antimonial minerals, 
315. Zinciferous minerals, 310. Plumbiferous 
minerals, 310. Regulus of Chili, 310. Slags of 
Copper, 310. Old Copper, 310. 


PAGE 

297 

297 


297 

299 

299 

299 


CONTEXTS. 


XX11L 


English Copper assay —continued : page 

Sect. IV. Summary considerations. Comparison of 
the results with the analysis in the wet way, 317. 
Conclusions, 318. 

German Copper assay . . . . .319 

Operations of this assay : — 

1. The roasting in the muffle furnace, 319. 

2. The solvent and reducing fusion, 321. 

3. The refining of the Copper on the cupel, or on the 


refining dish, 325. 

a. Refining upon the refining dish, 326. 

b. Refining on the cupel, 329. 

b. Assays for poor ores and products of Class I. . .331 

1. Concentration fusion, 311. 

2. Fusion with collecting agents, 332. 

c. Assays of oxidised ores and products of Class II. . . 333 

d. Assay of Copper alloys, Class III. . . 334 

Remarks upon the Copper assays in the dry way . . 335 

B. Assays in the wet way ..... 33G 

I. For substances rich in Copper . . . .336 

Kerl’s modified Swedish assay .... 336 

Assay of Copper by precipitation with metallic zinc . 341 

Colorimetric Copper assays . . . .342 

Heine’s colorimetric method, 343. 

Jacquelin’s and von Hubert’s method, 350. 


A. Muller’s assay with the complementary colorimeter, 354. 

Volumetric Copper assays .... 355 

Pelouze’s assay (precipitation analysis) with sulphide of 
sodium, 355. Ivunsel’s method for the estimation of 
Copper and nickel, and Copper and zinc, 357. Parkes’s 
and Mohr’s method by cyanide of potassium, 359. 
Schwarz’ method with the modification of Mohr, 361. 
Brown’s method by hyposulphite of soda, 362. Fleck’s 
modification of Mohr’s method, 363. Fleitman’s 
method, 364. 

Other Copper assays ..... 365 

Levol’s method, 365. Robert and Byer’s method, 365. 
Rivot’s method, 365. Chapman’s directions for the 
detection of minute traces of Copper in iron pyrites, 

366. Wolcott Gibbs’s electrolytic precipitation of 
Copper and nickel, 367. 

Blowpipe reactions of Copper . . . . .369 

Sulphide of Copper, 369. Argentiferous sulphide of Copper, 

369. Sulphide of antimony and Copper (bournonite), 369. 

Copper pyrites, sulphide of iron and Copper, 369. Sulphide 

of tin and Copper, tin pyrites, 373. Needle ore, aikenite, 

370. Chloride of Copper, 370. Carbonate of Copper, 370. 

Arseniate of Copper, 370. Oxide of Copper, 370. 




xxiv 


CONTENTS. 


CHAPTER X* 


Assay of Lead ....... 

Classification of minerals and substances containing Lead . 

Assay of substances of the first class (sulphides, antimonial, &c.) 

The action of various reagents upon sulphides of Lead :— 

Action of oxygen, 373. Action of metallic iron, 373. 
The alkalies and alkaline carbonates, 374. Nitrate of 
potash, 374. Argol, 374. 

3. Fusion with carbonate of potash, 375. 

2. Fusion with black flux, 382. 

3. Fusion with metallic iron, 383 . 

4. Fusion with carbonate of soda, or black flux and metallic 
iron, 385. 

5. Roasting and reducing assay, 387. 

G. Assay with sulphuric acid, 388. 

Assay of substances of the second class (plumbiferous substances 
containing neither sulphur nor arsenic, or mere traces only of 
these elements) ....... 

Ilumid assay of substances of the second class 

Assay of substances of the third class (substances into whose compo¬ 
sition either sulphuric, arsenic, chromic, or phosphoric acid, or a 
mixture of either, enters) ..... 

Humid assay of substances of the third class 
Assay of alloys of Lead (Class IV.) . 

Assay with sulphuric acid, 305. 

Additional remarks on the Lead assay .... 
Comparison of the different methods for the docimastic deter¬ 
mination of Lead in their application to various products, 395 . 
Markus’ comparative experiments :— 

a. Assay with black flux and iron, 305. 

b . Roasting and reduction assay with iron, 306. 

c. Roasting and fusing with black flux, 396. 

The results obtained, 39G. 

Levol’s fusion assay with ferrocyanide and cyanide of potassium 
Schemnitz Lead assay ...... 

determination of Lead by means of standard solutions 

1. Flores Dumonte’s method, 307. 

2. Schwarz’ method, 398. 

3. Ilempel’s method (modified) 401. 

Levol’s investigations, 402. 

Determination of Lead in the state of Carbonate 

Determination of Lead by oxalic acid .... 

Blowpipe reactions of Lead ...... 

Plumbiferous compounds, 405. Oxide of Lead, 40G. 

Ores of Lead :—Sulphide of Lead (galena), 406. Sulphate 
of Lead, 40G. Carbonate of Lead, 406. Phosphate o/ 
Lead, 406. 


FACE 

373 

373 

373 


390 

393 


393 

394 

395 

395 


397 

397 

397 


404 

405 
405 


CONTEXTS. 


XXV 


CHAPTER XI. 

PAGE 

The assay of Tin ....... 407 

Tin ores ........ 407 

Oxide of Tin, 407. 

Crystallised oxide of Tin, 407. Disseminated oxide of Tin, 

407. Sandy oxide of Tin, 407. Concretionary oxide of 


Tin, 407. 

Analysis of a sample of oxide of Tin from Cornwall, 408. 

Assay of pure oxide of Tin...... 408 

Method adopted in Cornwall, 408. Method by means of cyanide 
of potassium, 409. Winkler’s mode, 411. 

Assay of oxide of Tin mixed with silica . . . .411 

Assay of Tin ores containing silica, and Tin slags . . .412 

Assay of Tin ores containing arsenic, sulphur, and tungsten . 413 

Approximative assay . . . . . .414 

Estimation of Tin by the hum cl method .... 415 

Klaproth’s process, 416. 

Humid analysis of the alloy of Tin and iron as obtained in the 
treatment of siliceous ores and slags .... 417 

Estimation of Tin by means of standard solution . . .417 


Gaultier de Claubry’s process, 417. Scheurer Kestner’s pro¬ 
cess, 418, 419. Lenssen’s method, 418. Stromeyer’s me¬ 
thod, 419. Mohr’s experiments, 422. 

Blowpipe reactions of Tin ...... 425 

Tin pyrites, 425. Oxides of Tin, 426. 

CHAPTER XII. 

The assay of Antimony . . . . . .427 

Classification of antimonial substances . . . .427 

Class I. Native Antimony and all antimonial substances con¬ 
taining oxygen or chlorine, and but little or no sulphur: — 

Native Antimony, 427. Oxide of Antimony, 427. Anti- 
monious acid, 427. Antimonic acid, 427. 

Class II. Sulphide of Antimony, and all antimonial ores con¬ 
taining Sulphur :—Sulphide of Antimony, 427. Oxvsul- 
phide of Antimony, 427. Haidingerite, 427. 

Assay of ores of the first class ..... 427 

Assay of ores of the second class ..... 428 

1. Determination of the pure sulphide of Antimony (Anti- 

monium crudum) . . . . . .428 

2. Determination of regulus of Antimony . . .429 

Two methods, 429. 

a. By roasting and fusing the oxidised matter with 
black flux. 

h. By fusing the crude ore with iron, or iron scales, 
with or without the addition of black flux. 



XXVI 


CONTEXTS. 


TAOE 

Assaying sulphide of Antimony with cyanide of potassium . . 4.‘52 

Analysing sulphide of Antimony by boiling with aqua regia . 433 

Process in the assay of an antimonial ere . , . . 433 

Conversion of oxide of Antimony in alkaline solution into antiinonic 
acid by iodine (Mohr) ...... 434 

Distillation of ter- or penta-sulphide of Antimony with hydro¬ 
chloric acid, and titration of the evolved sulphuretted hydrogen 
(Schneider) ..... . . 434 

Blowpipe reactions of Antimony . . . . .435 

Bed and black sulphides of Antimony, 435. Antimony and its 
oxides, 435. 

CHAPTER XIII. 

The assay of Zinc ....... 437 

Classification of Zinc ores and zinciferous substances . . 437 

Class I. Zinc ores, in which the metal exists as oxide not 
combined with silica. 

Class II. Zinc ores, in which the metal exists as oxide, but 
partly or wholly combined with silica. . 

Class III. Zinc ores, in which the metal is partly or wholly 
combined with sulphur. 

Class IV. Alloys. 


Assay of ores of the first class ..... 437 

Determination of amount of Zinc by the humid process in ores of 
the first class , . . . . . . . 441 

Assay of ores of the second class ..... 442 

Humid determination of Zinc in ores of the second class . . 442 

Assay of ores of the third class . . . . .442 

Humid determination of Zinc in ores of the third class . . 443 

Assay of alloys (Class IV.) . . . . . .444 

Humid determination of Zinc in alloys .... 444 

Volumetric determination of Zinc ..... 444 


1. Method of Schafiher, modified by Kiinzel, 444. 

a. Solution of the ore, and preparation of the ammoniacal 

solution, 444. 

b. Preparation and standardising of the sulphide of sodium 

solution, 446. 

c. Determination of Zinc in the solution of the ore, 447. 

d. Further modification of the process. 

2. Schwarz’s method. 

3. Carl Mohr’s method. 

Blowpipe reactions of Zinc . . . . .451 

Zinc blende, black jack, 451. Carbonate of Zinc, calamine, 

451. Oxide of Zinc, 451. 




CONTEXTS. 


• • 


XXV11 


CHAPTER XIV 

PAGE 

Assay of Mercury ....... 453 

Mercurial ores . . . . . . .453 

Assay of mercurial ores . . . . . .453 

Assay for the amount of cinnabar in an ore . . . 45G 

Volumetric estimation of Mercury ..... 45G 

Persoline's process, 45G. 

Blowpipe reactions of Mercury ..... 4G0 


Mercury, 4G0. Cinnabar, 4G0. Chloride of Mercury, horn 
Mercury, 460. 

CHAPTER XV. 


Assay of Silver ....... 

Classifications of the argentiferous substances 
Class I. All minerals containing Silver. 

Class II. Metallic Silver and alloys. 

General observations on the assay of ores and subst-mces of Class I. 
Fusion with oxidising reagents ..... 

Litharge, 4G3. 

Special directions for the crucible assay of ores and substances of 
Class I. ....... 

Preliminary assay for dividing all substances of this class into 
three sections, 4G6. Assay of oxidising power of nitrate of 
potash, 4G8. Assay of litharge for Silver, 4G8. Assay of 
reducing power of argol, 4G8. 

Assay of ores of the first section ..... 

Assay of ores of the second section .... 

Assay of ores of the third section .... 

* 

Scoritication ... . . . . 

Three distinct periods in the operation : viz. the roasting, the 
fusion, and the scorification, 472. 

Special instructions for the scorification assay of ores of Class I. 
Assay in scoritier, 47G. 

Assay of substances of the first class mixed with native, or metallic 
Silver ........ 

Cupellation ....... 

Amalgamation ....... 

Separating Silver from galena ..... 

Assay of substances of the second class .... 

General remarks on the assay of the alloys of silver and copper 

Cupellation, 487. Quantity of Lead required, 488. Loss of 
Silver in the assay of coined alloys, 490. 

Special instructions for the assay of the alloys of Silver and copper . 
Assay for approximative quantity of alloy, 491. Assay proper 
of Silver bullion, 491. Assay of alloys of copper and Silver, 
192. 


461 

4G1 


G41 

4G3 


4GG 

tf 


4G9 

4G9 

470 

470 


475 


47G 
478 
48 G 
487 
487 
487 


491 







XXV111 


CONTENTS. 


Assay of alloys of platinum and Silver . 

Assay of alloys of platinum, Silver and copper 

Assay of native Silver, rough Silver left on sieve during pulverisa¬ 
tion of Silver ores of first class and native alloys 

Dyce’s process for separating gold and Silver from the baser 
metals 

Assay of Silver bullion by the wet way .... 

Gay-Lussac’s process ...... 

Measurement of the solution of common salt, 49G. Measure of 
the normal solution of salt by weight, 49G. Preparation of 
the’decime solution of common salt, 498. Preparation of 
the decime solution of Silver, 499. Weighing the normal 
solution of common salt, 500. Preparation of the normal 
solution of common salt when measured by weight, 501. 
Preservation of the normal solution of common salt, 505. 
Application of the process described in the determination of 
the standard of a Silver alloy, 507. Measuring the normal 
solution of common salt by volume, 509. Methods of mea¬ 
surement in the employment of volumes instead of weights, 
509. Temperature of the solution, 514. Preservation of 
the normal solution of salt in metallic vessels, 515. Prepa¬ 
ration of the normal solution of salt, measuring by volume, 
517. Correction of the standard of the normal solution of 
salt when the temperature varies, 520. Table of correction 
for variations in temperature of the normal salt solutions, 
522. 

Table for the assay, by the wet method, of an alloy containing 
any proportions whatever of Silver, by the employment of a 
constant measure of the normal solution of common salt, 522. 
Tables for determining the standard of any Silver alloy by em¬ 
ploying an amount of alloy always approximatively containing 
the same amount of Silver, 52G-535. 

Tables for determining the standard solution of any Silver alloy 
by employing an amount of alloy always approximately con¬ 
taining the same amount of Silver, 536-545. 

Application of Gay-Lussac’s process .... 

Assay of pure, or nearly pure Silver, the temperature of the normal 
solution of salt being that at which it was standardised . 

First example, 546. Second example, 547. Third example, 
548. 

Graduation of the normal solution of salt, the temperature being 
different to that at which it is wished to he graduated 
First method, 549. Second method, 550. 

Approximative determination of the standard of an unknown alloy . 

Modes of abridging manipulations ..... 
Bottles, 551. Water-bath, 552. Flue, 553. Agitator, 553. 
Table, 551. Cleansing the bottles, 55G. 


PACE 

492 

493 

493 

493 

494 
494 


546 

54G 


549 

550 

551 


CONTEXTS. 


XXIX 


Reduction of chloride of Silver obtained in the assay of alloys by the 
wet way ....... 

Preparation of pure Silver ...... 

Modifications required in the assay of Silver alloys containing mer¬ 
cury ........ 

Appendix :— 

Apparatus for washing the normal solution of salt 

Apparatus for filling the pipette with normal solution by aspira¬ 
tion, and for convenient adjustment.... 

Another apparatus for filling the pipett 3 with normal solution 
of salt ....... 

Apparatus for preserving the normal solution of salt at a 
constant temperature ..... 

Means of protection from the nitrous vapours disengaged from 
the bottles during the process of assay by the humid method 

Method of taking the assay from the ingot 

Estimation of Silver in ores and alloys, by iodide of starch; 
methods of Pisani and Field .... 

Assay of commercial Silver, Gay-Lussac’s method modified by 
Mulder ....... 

Three different ways for the assay of silver, 571. Standard 
solution of salt, 572. Decimal solution of salt, 573. 
Dropping apparatus for concluding the assay, 574. Titra¬ 
tion of the standard solution of salt, 574. 

Blowpipe reactions of Silver ..... 

Sulphide of Silver, 57G. Red Silver, 57G. Antimonial Silver, 
and argentiferous antimony, 57G. Electrum, 577. Amalgam, 
577. Chloride of Silver, horn Silver, 577. Oxide of 
Silver, 577. 

David Forbes’s researches on the application of the blowpipe to the 
assay of Silver ....... 

The apparatus used for the operations, 579. Concentration of 
the Silver-lead, 580. Cupellation, 582. Determination of 
the weight of the Silver globules obtained on cupellation, 585. 
The scale for this purpose, 587. Table showing the weight 
of globules of different diameters, 588. Cupellation loss, 
589. Table showing the respective amount, 591. 

Classification of argentiferous substances, 592. 

A. Metallic alloys capable of direct cupellation, 592. 

a. Consisting chiefly of lead or bismuth, 592. 

b. Consisting chiefly of Silver : native Silver, bar, test, and 
precipitated Silver, retorted Silver amalgam, standard 
Silver, Silver coin, and other alloys of Silver with gold 
and copper, 593. 

c. Containing chiefly copper: native copper, ingot, wire, 
or sheet copper, cement copper, copper coins, copper- 
nickel alloys, 594. 


PAim 

55G 

557 

558 

559 
5G0 
561 
5G2 

563 

564 

5G7 

569 

576 

577 


XXX 


CONTEXTS. 


Classification of argentiferous substances— continued — 

13. Metallic alloys incapable of direct cupellation, 595. 

a. Containing much copper or nickel, with frequently some 
little sulphur, arsenic, zinc, iron, cobalt, &c., as un¬ 
refined or black copper, brass, German silver, &c., 595. 

1. Containing tin : argentiferous tin, bronze, bell and gun 
metal, bronze coinage, &c., 59G. 

c. Metallic alloys containing much antimony, tellurium, 
or zinc, antimonial Silver, and argentiferous antimony, 
telluric Silver, and argentiferous zinc, 595. 

d. Compounds of Silver with mercury: arquerite, native 
and artificial amalgams and argentiferous mercury, 599. 

e. Compounds chiefly consisting of iron: argentiferous 
steel, cast iron, bears from smelting furnaces, GOO. 


CHAPTER XVI. 


The assay of Gold ....... 

Classification of the substances containing Gold 

Class I. Substances containing Gold in a minute state of 
division. 

Class II. All alloys of Gold, native or otherwise. 

Assay of substances of the first class .... 

Substances of the second class ..... 
Description of native Gold, and analyses of several varieties of 
native Gold, G03. Analyses of some Gold alloys, G05. 
Standard Gold of England, GOG. 

General observations on the assay of Gold alloys 

Cupellation, Gold and lead, GOG. Gold and copper, proportion 
of lead, G07. The examination on the touchstone, G08. 
Tables for proportion of Lead to be employed in the cupella¬ 
tion of Gold and copper, G10. Gold, silver, platinum, and 
copper, G10. 

Parting of gold from silver in the wet way .... 
Inquartation, G12. Operation, G13. Surcharge, G14. State¬ 
ments referring to this subject, G14. 

Assay of Gold produced from auriferous ores 

By means of nitric acid, 615. Employment of aqua regia, 616. 
By means of the standard solution of sea-salt, GIG. Nickles’ 
remarks on the parting process, GIG. Rose’s method, 617. 

Standard of the alloys of Gold ..... 

Assay of the alloys of Gold and copper .... 
Preliminary assay, G18. Assay proper, G19. Parting assays, 
G21. 

Assay of tellurides and other native mineralised substances con¬ 
taining Gold ....... 

Blowpipe reactions of Gold ..... 

Graphic Gold, 623. Telluriferous and plumbiferous Gold. 


l’A(tE 


G02 

G02 


G02 

G03 

GOG 

612 

615 

618 

618 

623 

G23 


CONTENTS. 


NXX1 


CHAPTER XVII. 

PAGE 

The assay of Platinum ...... 624 

Platinum in its native state ..... 624 

_ 9 

Analysis of Platinum ores . . . . . .624 

Berzelius’ method, 624. Plans for detecting Platinum in ad¬ 
mixture with gold and other heavy matters, 632. Deville 
and Debray’s method of analysis of Platinum ores, 633. 
Analysis of Platinum ores from various sources, 637. 
Guyard’s process for the extraction of metals from platini- 
ferous residues, 637. 

CHAPTER XVIII. 


The assay of Bismuth . . . . . .641 

Varieties of Bismuth ores ...... 641 

Assay of native Bismuth . . . . .641 

Assay of Bismuth residues, cupel bottoms, &c. . . .641 

Determination of amount of Bismuth by the humid process . 642 

Balard’s industrial analysis of old type metal . . . 642 

Pearson’s process for the assay of Bismuth by weight and by 
volume ........ 643 

Preparation of standard solution, 643. 

Blowpipe reactions of Bismuth ..... 644 


Native Bismuth, 644. Sulphide of Bismuth, 644. Oxide of 
Bismuth, 644. 

Distinguishing Bismuth from antimony and tellurium, 644. 

* 

CHAPTER XIX. 


The assay of Chromium . . . . . .646 

Principal ore of Chromium ..... 646 

Analyses of it, 646. 

Assay of chrome ore • . . . . . .646 

Clarke’s process ....... 647 

Determination of Chromium by means of standard solution . 649 

Blowjhpe reactions of Chromium . . . . .650 

Chrome ochre, 650. Oxide of Chromium, 650. 


CHAPTER XX. 

The assay of Arsenic . . . • • .651 

Minerals from which Arsenic is produced • . . *651 

Assay for Arsenic . » . . . • .651 

Approximative assay, 651. Improved method, 652. 

b 



CONTEXTS. 


xxxii 


CHAPTER XXI. 


PAGE 

The assay of Manganese . • . * . 


653 

Commercially valuable minerals containing Manganese 


653 

Assay of Manganese ores .... 


653 

Thompson’s method .... 


655 

Fresenius and Will’s method . 


656 

Blowpipe reactions of Manganese . 


660 

Sulphide of Manganese, 650. Peroxide of Manganese, 650 
Oxides of Manganese, 650. 


CHAPTER XXII. 

The assay of Cohalt and Nickel ores 

• • 

662 

Ores of Cobalt ..... 

• • 

662 

Ores of Nickel ..... 

• • 

662 

Assay for Cobalt ..... 

• • 

662 

Liebig’s method of separating Nickel from Cobalt . 

• • 

664 

Wolcott Gibbs’s improvement on Liebig’s method . 

• • 

664 

Terreil’s method for separating Nickel from Cobalt . 

• • 

665 

Blowpipe reactions of Cobalt 

• • 

666 


Sulphide of Cobalt, 666. Arsenical Cobalt, 667. Cobalt glance, 
667. Black oxide of Cobalt, 667. Arseniate of cobalt, 667. 
Oxide of Cobalt, 667. 


Blowpipe reactions of Nickel ..... 668 

Arsenical Nickel, 668. Sulphide of Nickel, 668. Oxide of 
Nickel, 668. 

Plattner’s method for detecting Nickel when contained in large quan¬ 
tities of Cobalt . . . . . .669 


CHAPTER XXIII, 


The assay of Sulphur . . . . .671 

The commercially valuable Sulphur minerals . . .671 

Distilling assay to approximatively estimate the value of these ores . 671 

Four assays required to fully ascertain the value of a Sulphur ore . 672 

The assay of Sulphur in the wet way .... 672 


CHAPTER XXIV. 

Discrimination of Gems and Precious Stones . . . 674 

Explanation and introduction, 674. Principal sources of 
’recognition of gems, ’674. The specific gravity of sub¬ 
stances, and its determination, 674. 







CONTEXTS. 


XXXlll 

PAGE 

Colourless stones ....... 676 

The diamond, 674. Quartz, 675. White zircon, 678. White 
sapphire, 679. White topaz, 679. Comparative table of 
the weights of colourless stones weighed in air and water, 681. 

The use of the table, 680. 

Yellow stones ....... 682 

Yellow zircon, 682. Yellow sapphire, 682. Cymophane, 682. 
Yellow topaz, 683. Yellow tourmaline, 683. Yellow eme¬ 
rald, 684. Yellow quartz, 685. Comparative table of the 
weights of yellow stones in air and water, 686. 

Brown and flame-coloured stones ..... 686 

Zircon (hyacinth), 686. Vermeil garnet, noble garnet, alman- 
dine, 686. Essonite, cinnamon stone, 688. Tourmaline, 

688. Comparative table of the weights of brownish and 
flame-coloured stones, weighed in air and water, 688. 

Red and. rose-coloured stones ..... 689 

Red sapphire, 689. Deep red garnet, noble garnet, 689. Ruby 
(spinel), 689. Reddish topaz, 689. Red tourmaline, 689. 
Comparative table of the weights of these stones in air and 
water, 690. 

Blue stones ....... 690 

Blue sapphire, 690. Disthene, cyanite, 690. Blue topaz, 691. 

Blue tourmaline, 691. Blue beryl, 691. Dichroite, water 
sapphire, 691. Turquoise, 692. Comparative table of the 
weights of blue stones, weighed in air and water, 692. 

Violet stones . . . . . . . 693 

Violet sapphire, 693. Violet tourmaline, 693. Violet quartz, 
amethyst, 693. Comparative table of the weights of violet 
stones, weighed in air and water, 693. 

Green stones ....... 694 

Green sapphire, 694. Peridot, crysolite, 694. Green tourma¬ 
line, 694. Emerald, 694. Aqua marine, 694. Chryso- 
prase, 694. Comparative table of the weights of green 
stones weighed in air and water, 695. 

Stones possessing a play of colours (chatoyant) . . .695 

Sapphire, 696. Garnet, 696. Cymophane, 696. Antique 
emerald, 696. Quartz, 696. Felspar, nacreous felspar, fish- 
eye, &c., 696. Comparative table of the weights of stones , 
possessing a play of colours (chatoyant), weighed in air and 
water, 697. 



XXXIV 


CONTENTS. 


APPENDIX. 


Table I. Showing the quantity of fine gold in 1 oz. of 
any alloy to ^ of a carat grain, and the mint 
value of 1 oz. of each alloy . 

Tables A, B, and C. To convert mint value into bank value, 
when the standard is expressed in carats, 

. grains, and eights .... 

Table II. Table of relative proportions of fine gold and 
alloy, with the respective mint values of 1 oz. 
of each alloy when the standard is expressed 
in thousandths .... xxi- 

Table. To convert mint value into bank value when the 
standard is expressed in thousandths 

Table III. Assay table, showing the amount of gold and 
silver, in ounces, pennyweights, and grains, 
contained in a tone of ore, &c., from the 
weight of metal obtained in an assay of 200 
grains of mineral . . , xxxiv 


PAGE 


11 —xix 


XX 


-xxxii 

xxxiii 


xlvii 


MANUAL 



OF 

PRACTICAL ASSAYING. 

-»< > ♦ — ■■■ — 

CHAPTER I. 

CHEMICAL NOMENCLATURE : LAWS OF COMBINATION : ETC. 

It is not necessary, neither is it possible, in a treatise like the 
present, to give more than a very brief outline of the 
elements of chemical nomenclature, and the more simple 
laws of chemical combination. Undoubtedly a knowledge 
of chemistry is of the greatest value to the practical assayer 
—indeed, we may say no one can attain to any degree of 
eminence in this branch of industry unless he has had some 
amount of practice in the laboratory. But it will be quite 
beyond our province here to teacli the elements of chemistry. 
So much of the nomenclature and leading laws will be 
given as are indispensable to a proper understanding of 
what is to follow, but beyond this the student must seek for 
further instruction in chemistry from books which are 
specially devoted to that science; and he should above all 
things endeavour to acquire a practical acquaintance with 
the laws and manipulations of experimental chemistry, by 
taking a series of lessons in a laboratory. 

Chemical Nomenclature. —Every material substance with 
which we are acquainted consists of one or more bodies, 
termed simple or elementary —such bodies being so called 
from the fact that with our present means of research we 
are unable to reduce them to a more simple form. Thus, 
if a piece of common iron pyrites, or mundic, as it is 

B 






2 


CHEMICAL NOMENCLATURE. 


commonly called, be submitted to certain operations, it 
will be found that we can obtain from it two substances 
totally distinct, in both physical and chemical properties, 
from each other and from the substance from which they 
were obtained. One body is sulphur , an opaque yellow 
substance, fusing at a very low temperature, igniting 
readily, and exhaling when burning a peculiar and suffo¬ 
cating odour. The other constituent of the pyrites is 
iron , a well-known metallic substance, requiring an intense 
heat for fusion, and becoming red-hot without burning. 
If we were now to perform any experiment which, in the 
present state of knowledge, ingenuity could suggest, we 
should be totally unable to cause either the sulphur or the 
iron to assume a more simple or elementary state of existence. 
We can with ease cause either of them to enter into new 
combinations with other bodies, and these compounds we can 
decompose—as in the case of the pyrites—and obtain both 
sulphur and iron again in their separate forms with all their 
characteristic properties ; but nothing more than this can be 
effected : hence we are led to the belief that both sulphur 
and iron are simple bodies, or bodies containing only one 
kind of matter. 

The following is a list of the simple substances discovered 
up to the present time; it is accompanied by certain 
symbols and numbers, the use and nature of which will be 
hereafter pointed out. Those substances in italics have 
hitherto found no practical use; and those marked with 
an asterisk (*) are often found native, or unassociated with 
mineralising elements. 

The first column contains the common name of the 
element; the second, the symbol, or chemical short-hand 
character, in which all chemical changes and decomposi¬ 
tions are most readily written and understood; and the 
third, the atomic weights. These atomic weights are not 
absolutely correct: they are not given beyond the first place 
of decimals, to avoid tedious calculation. For all practical 
purposes they may be considered accurate. Of the compounds 
of these elements, only those will be discussed which are 
likely to fall under the notice of the assayer. 


CHEMICAL NOMENCLATURE. 


3 


Non-Metallic Elements or Metalloids. 


Names of the 
Elements 

Symbols 

Atomic 

Weights 

Names of the 
Elements 

Symbols 

Atomic 

Weights 

Oxygen . 

0 

B 

Selenium . 

Se 

39-7 

Hydrogen . 

H 

1 

Tellurium . 

Te 

64-5 

Nitrogen . 

N 

14 

Phosphorus 

P 

31 

Fluorine . 

FI 

19 

Arsenic 

As 

75 

Chlorine . 

Cl 

35*5 

* Carbon 

C 

0 

Bromine . 

Br 

80 

Boron 

B 

11 

Iodine 

I 

127 

Silicium 

Si 

14 

* Sulphur 

S 

10 

Zirconium . 

Zr 

44-8 


Metallic Elements. 


Names of the 
Elements 

Symbols 

Atomic 

Weights 

Names of the 
Elements 


Symbols 

Atomic 
Weights , 

Potassium . 

K 

39-1 

Nickel 


Ni 

29-5 

Sodium 

Na 

23 

Zinc . 


Zn 

32-0 

Lithium 

Li 

7 

Cadmium . 


Cd 

50 

\ Barium 

Ba 

68-5 

*Copper 


Cu 

31-7 

1 Strontium . 

Sr 

43-8 

Lead. 


Pb 

103-5 

Calcium 

Ca 

20 

Thallium . 


T1 

203 

Magnesium 

Mg 

12 

*Bismuth . 


Bi 

210 

Aluminium 

A1 

13-5 

Tin . 


Sn 

59 

Glucinurn . 

Be 

4-7 

Titanium . 


Ti 

25 

Cerium 

Ce 

46 

Tungsten . 


AY 

92 

Lanthanum 

La 

40 

Molybdenum 


Mo 

48 

Didymium . 
Yttrium 

Di 

48 

Vanadium . 


V 

08-0 



Antimony . 


Sb 

122 

Erbium 

Er 


♦Mercury . 


Hg 

100 

Terbium 

Tr 


* Silver 


Ag 

108 

Niobium 

Nb 


* Rhodium . 


Pth 

52-2 

Tantalum . 

Ta 

37-6 

* Palladium . 


Pd 

53-3 

Thorium . 

Th 

59-5 | 

* Platinum . 


Pt 

98-7 

Manganese 

Mn 

27-5 

* Ir idiu m 


Ir 

99 

Chromium 

Cr 

26-7 

* Ruthenium 


Ru 

52-2 

Uranium . 

U 

60 

* Osmium 


Os 

99-0 

Iron . 

Cobalt 

Fe 

Co 

28 

29-5 

♦Gold . . 


An 

197 


The principal compound bodies are acids, oxides, salts, 
and binary substances containing no oxygen. 

When a body combines in more than one proportion with 
oxygen, that compound containing the least oxygen takes 
the termination ous, that the most ic ; thus, sulphurous 
acid, sulphuric acid ; arsenious acid, arsenic acid ; ferrous 
oxide, ferric oxide; mercurous oxide ; in only one propor¬ 
tion (or when they form only one basic oxide) they are 
distinguished by the termination ic , as potassic oxide, 
aluminie oxide. 

15 2 
































































4 


ACIDS AND SALTS. 


Oxides are binary oxygen compounds: they may be 
divided into two series. The first comprises those oxides 
which do not possess the property of combining with acids 
to form salts—they are termed indifferent oxides ; the 
second series contains those capable of uniting with acids 
to form salts, and are called salifiable oxides or bases . 

When a simple body, in combining with oxygen, forms 
but one oxide, it is simply called an oxide ; added to the 
name of the simple body ; thus, oxide of zinc or zincic 
oxide. 

If the body is capable of combining with oxygen in many 
proportions, the words proto, sesqui , bin or per , &c., precede 
the term oxide to express the progressive amounts of oxygen. 
Most metals form one salifiable oxide, and many of them have 
two. These are now generally distinguished by the termi¬ 
nations ous and zc, in the same manner as are the acids ; 
thus, we have protoxide of lead, iron, copper, tin, &c.; sesqui - 
oxide of aluminium, iron or chromium, &c. ; binoxide , or 
peroxide of manganese, copper, mercury, &c.; and when we 
speak of them as salifiable bases, ferrous oxide and ferric 
oxide ; mercurous and mercuric oxide ; potassic oxide ; 
aluminic oxide. 

There are still higher degrees of oxidation of some metals ; 
these are nearly always acids—as chromic, stannic, and 
antimonic acids. 

Salts are formed when an acid unites with a base, and 
usually the properties of the acid and the base are reci¬ 
procally neutralised ; thus, an acid which before combina¬ 
tion possessed the power of reddening blue litmus, loses it 
in proportion as it combines with the base ; and in like 
manner a base which would at first change reddened 
litmus paper to blue, loses this property as the acid satu¬ 
rates it. In this case the acid and base have combined 
to form a salt. 

In naming salts, we have to consider—firstly, the nature 
of the acid; secondly, the salifiable nature of the base; 
and thirdly, the proportions in which the acid and base are 
combined. 


Acids terminating in ic form salts terminating in ate. 


LAWS OF COMBINATION. 


5 

Acids terminating in ous form salts terminating in ite ; 
and the new names terminating in ate and ite are added to 
the name of the compound oxide. Thus, sulphuric acid and 
protoxide of iron form sulphate of protoxide of iron, ferrous 
sulphate, or, more commonly, protosulphate of iron. Arse- 
nious acid and protoxide of iron form arsenite of protoxide 
of iron, ferrous arsenite, or protarsenite of iron; nitric acid 
and sesquioxide of iron, nitrate of sesquioxide of iron or 
ferric nitrate. 

When the salt formed exists in the neutral state, its name 
is formed as above ; but if the proportion of acid is larger 
than in neutral salts, it is termed an acid salt : thus we 
have acid sulphate of potash. 

If the base is in excess, the name is preceded by sub : 
thus, subacetate of lead. This class of salt is also called 
basic. 

Binary Compounds containing no Oxygen. —These com¬ 
pounds exist very largely in nature, and it is from them we 
obtain the greater part of our copper, lead, silver, &c. 

When a metalloid combines with a metal to form a com¬ 
pound which is neither acid nor basic, its name is derived 
from the metalloid by the addition of the termination uret 
or ide. The latter is more usually employed by chemists; 
the former by miners and mineralogists. The latter term is 
however gradually displacing the former, and is now seldom 
applied except to the sulphur compounds, and in these one 
term is as often used as the other; for the sake of unifor¬ 
mity, it is much to be desired that the termination uret 
should be discontinued altogether. Thus the compounds 
of sulphur and chlorine with iron and silver, are called 
sulphuret or sulphide of iron, cldoride of silver, &c. 

If a metalloid combines witli a metal in more than one 
proportion, the same rule is followed as in the oxygen com¬ 
pounds ; thus we have proto-sulpliide of iron, sos^z-sulphide 
of iron, and W-sulphide of iron (ordinary iron pyrites or 
mundic). 

Laws of Combination. —On examining the variety of com¬ 
pounds which the same substances may afford by their union 
in different proportions, it has been discovered that the pro- 


G 


COMBINING PROPORTIONS. 


portions of the elements existing in each compound are 
definite; a certain weight of one substance will only 
combine with a certain weight or weights of another 
substance, and the lowest combining weight of any of the 
elementary bodies is termed its equivalent or atomic weight , 
and is represented by the numbers in the third column of 
the table of elementary substances. 

As before stated, all substances combine in fixed or defi¬ 
nite proportions; thus, if 1114 parts of oxide of lead were 
analysed, they will be found to consist of 103^ parts of lead 
and 8 of oxygen. Again, the analysis of 9 parts of water or 
oxide of hydrogen would give 1 part of hydrogen and 8 of 
oxygen ; now, assuming, as in the table of equivalents, hy¬ 
drogen to be unity, we have 103-5 as the equivalent of lead, 
and 8 as that of oxygen. Tf we follow oxygen further 
in its combinations, it will be seen that it combines thus :— 


8 parts of Oxygen combine with 


V 

V 

V 

r> 

V 

V 

>> 

>> 

V 

V 


)•> 


1 part of Hydrogen 
103*5 „ Lead 

20 „ Calcium 

59 „ Tin 

31*7 „ Copper 


The above numbers, therefore, represent the equivalents 
of the substances to which they are appended. 

Again, the equivalent of sulphur is 16, and that weight of 
sulphur combines with the above weights of hydrogen, lead, 
calcium, tin, and copper to form sulphides of the respective 
bases. 35*5 parts of chlorine, or 39*7 parts of selenium, also 
combine with the same weights, viz. hydrogen 1, lead 103*5, 
&c., to form chlorides and selenides. 

Such compounds are of the simplest class, consisting of 
single equivalents only ; there are, however, many bodies 
containing more equivalents than two, in which case the 
following laws are followed. 

In one class of compounds the quantity of one of the 
constituent elements remains constant, while each new com¬ 
pound is formed by the gradual addition of another equivalent 
of the other constituent element; and it must be borne in 
mind that no element combines with another in less quantity 
than its equivalent proportion. 


COMBINING PROPORTIONS. 


7 


Another series of compounds commences with two equi¬ 
valents of an element united with some uneven number of 
equivalents of another element. 

In these cases the ratio may be as 2 to 3 and 2 to 5. 

The equivalent of a compound body is the sum of the 
equivalents of the elements forming it; thus, sulphuric acid is 
composed of one equivalent or 16 parts of sulphur, and three 
equivalents or 24 parts of oxygen ; its equivalent is therefore 
40 ; potash is composed of 39*1 parts of potassium and 8 of 
oxygen = 47*1. Now, sulphuric acid combines with potash 
to form sulphate of potash, the equivalent of which is 87*1. 
In this manner the equivalent of any compound body may 
be ascertained by adding together the equivalents of the 
substances forming it. 

From what has just been stated concerning the constancy 
of composition of chemical compounds, we are enabled to 
calculate the reaction occurring between two or more bodies 
when decomposition takes place ; thus, 87*1 parts of sul¬ 
phate of potash contain 40 parts of sulphuric acid and 47*1 
parts of potash ; and if it were desired to obtain sulphate of 
lead by the decomposition of nitrate of lead by adding to it 
the above quantity of sulphate of potash, the exact amount of 
nitrate of lead required could be readily found by adding 
together the equivalent of the elements foraging nitric acid 
and oxide of lead. Thus, nitric acid is composed of 14 
nitrogen and five equivalents of oxygen, or 40, together 54 ; 
oxide of lead of 103-5 of lead, and 8 oxygen, together 111*5, 
which, with the nitric acid, form 165*5. Now, on the addition 
of 165-5 parts of nitrate of lead in solution to 87*1 parts 
of sulphate of potash also dissolved in water, 151*5 parts of 
sulphate of lead will be precipitated in the insoluble form, 
and 101*1 of nitrate of potash remain in solution. 

Chemical Symbols : their use.— The symbol of an element 

%/ 

standing alone signifies one equivalent or atom of the sub¬ 
stance; thus, S implies 16 parts of sulphur : a small figure 
on the right hand side of the symbol indicates the number 
of equivalents to be represented, as S 2 , equal to two equiva¬ 
lents, or 32 parts of sulphur. 

Two symbols placed thus, FeS, indicate a compound of 



8 


CHEMICAL SYMBOLS. 


iron and sulphur, one equivalent of each. Separation of 
elements by the sign + or a comma, is employed to show 
the union of two compound bodies, as sulphide of silver 
and sulphide of lead, which compound may be thus written, 
AgS 4 - PbS, or AgS, PbS. A large figure on the same 
line as the symbol, and on its left side, multiplies the whole 
of the 'symbols to the first comma or -f sign; thus, 
2AgS,PbS or 2AgS -f PbS represents a compound of two 
equivalents of sulphide of silver, with one of sulphide of lead ; 
if, however, it be thus written 2(AgS,PbS) it means two 
equivalents of the whole of the elements which are enclosed 
in the brackets. 


CHAPTER II. 


PREPARATION OF THE SAMPLE—WEIGHING. 

In all operations connected with assaying, the selection of 
the sample is the first and most important. It is of little 
use for the operator to ascertain with the utmost accuracy 
the percentage of every individual constituent in the 
mineral operated on, if his sample does not truly, represent 
the average quality of the ore. It should be borne in mind 
that samples of mineral are generally pieces selected for 
their richness, or at all events that they represent the most 
favourable portions of the ore; and no pains should be spared 
to secure a sample for analysis which will truly represent 
the bulk of mineral whose value is required to be known. 

The assayer should always bear in mind the object which 
his experiments have in view. If they are to ascertain the 
actual percentage of one or more constituents existing in a 
certain stone, his labours are comparatively easy,—all that 
is required being to reduce the whole of the specimen to the 
finest possible state of division, and having well mixed the 
powder, to analyse a portion of it. 

But if it is desired to find out the composition of a 
mineral or crystal, the greatest possible care must be taken 
to remove every particle of gangue or other impurities, and 
to obtain for analysis those portions only of the specimen 
which represent with greatest accuracy the pure mineral. 
To effect this, the surrounding rock is first to be removed as 
carefully as possible, and then the specimen crushed into 
coarse pieces on a sheet of clean paper. By means of a 
pocket magnifier and a pair of pincers, clean, typical pieces 
of the mineral are then to be selected for analysis. 

If, however as will most frequently be the case, the object 


10 PREPARATION OF TIIE SAMPLE. 

of the assay be to ascertain the average value of a mineral 
lode or heap of ore, then the assayer must proceed differ¬ 
ently. The portion experimented upon must truly represent, 
in the respective amounts of its valuable material, gangue, 
quartz, and earthy matters, the great bulk of that of which it 
professes to be a sample; and this having been secured, the 
whole must be carefully powdered and passed through fine 
sieves, taking care that every portion of the mineral goes 
through. If this be not attended to it will frequently happen 
that the few grains left out are sufficient to vitiate the 
whole assay: this is especially liable to be the case when 
examining ores, the valuable ingredients of which are of a 
ductile or malleable nature, such as auriferous quartz. In 
this case it frequently happens that the great bulk of gold 
exists in the form of one or two small pieces, and these being 
flattened and beaten out in the operation of powdering will 
almost certainly be left upon the sieve. In cases like this it 
is better to collect and assay such pieces separately, and 
estimate their proportion to the whole weight of the sample, 
than to attempt to powder and distribute them uniformly. 

The ore must always be reduced to a pulverulent form, 
more or less fine, according to the nature of the chemical 
operation or assay to which it is to be further subjected. 
This division is effected by means of the anvil, hammer, 
pestle and mortar, sieve, method of decantation, or other 
means generally in use for the preparation of any fine 
powder. The actual process to be adopted must vary ac¬ 
cording to the nature of the different bodies under examina¬ 
tion. In some cases simple crushing is sufficient; in others 
the ore will have to be pounded in a mortar; whilst occa¬ 
sionally it is necessary to reduce it to the very highest degree 
of fineness by elutriation. There is also another operation, 
which is as strictly mechanical as are the above, viz. wash¬ 
ing, dressing, or vanning a sample of ore, the end and aim 
of which is to separate, in a suitable vessel, by means of water 
and difference of specific gravity, the earthy or useless, and, 
in some cases, objectionable portion, from the heavier metallic 
and valuable portion. This operation is almost always em¬ 
ployed on the larger scale in dressing ores for the smelter. 


ANVIL AND STAND. 


11 


The tools and materials employed are the anvil (and 
stand), vice, hammer , files , cold chisel , shears , pestle and 
mortar , crushing mortar , sieve, &c. 

The Anvil and Stand (Fig. 1). —The anvil-stand is con¬ 
structed of stout wood, about two inches in thickness, and 
forms a cube of about two feet square. It contains three 
or four drawers, which serve to hold the hammers, cold 


Fig. 1. 



chisels, shears, files, &c. which are required in an assay 
office. In the centre is firmly fixed the anvil, and in one 
corner a vice may be also firmly secured. 

In General the anvil and hammer are employed for the 
purpose of breaking a small fragment from a mass of ore for 
examination, or ascertaining whether the button or prill of 
metal produced in an assay be malleable or otherwise. The 
anvil is also exceedingly useful as a support for a crucible 
while breaking it to extract the metallic or other valuable 

contents. 

The anvil is most useful in size when it weighs about 
28 lbs. ; but one of 14 lbs. will suffice. By reference to the 
flexure it will be seen that the anvil recommended is of the 
shape usually employed by the blacksmith. 




















































12 USE OF ANVIL, HAMMERS, ETC. 

and 3, of which two are requisite, 
ought to have one end flat and 
square and the other pick or wedge 
shaped. The horizontal wedge end 
of fig. 2 is useful for breaking open 
crucibles, and detaching small 
fragments from a specimen of ore 
the flat end for ascertaining the 
malleability of buttons of metal. 
This hammer should weigh about 
1 lb. The larger hammer, fig. 3, 
should weigh about 4 lbs., and is 
employed for breaking coke suffi¬ 
ciently fme for the use of the fur¬ 
nace, and detaching fragments from 
refractory minerals, in both of 
which cases either end may be employed, as may seem most 
serviceable to the operator. The flat end of this hammer is 
also used for driving a cold chisel in separating masses of 
gold, silver, copper, lead, &c. for assay. This hammer has 
a vertical pick or wedge end. 

Very hard and stony materials which have to be broken on 
the anvil (and all such ought to be so treated) scatter many 
fragments, to the certain loss of a portion of the substance, 
and the probable injury of the operator ; this can be pre¬ 
vented by wrapping the mineral in a piece of stout brown 
paper, or, if necessary, in several folds. The fracture can 
then be safely attempted. 

This latter precaution must be specially taken in fractur¬ 
ing gold quartz, or hard rock containing metallic silver, as 
the loss of a very minute quantity of metal would involve a 
considerable error in the result afforded by the assay. 

All minerals, however, unless very friable, must be re¬ 
duced to a moderate size—say that of a walnut—by means 
of the anvil and hammer, before pulverisation; other¬ 
wise, if the reduction be attempted in a mortar, it is nearly 
certain to be injured; moreover, the operator will find his 
labours much abridged by using the anvil for this purpose. 

The anvil can also be made very serviceable in repointing 


The hammers, ligs. 2 

Fio. 2. Fio. 3. 




PULVERISATION OF THE SAMPLE. 


13 


worn or burnt-out tongs, &c. It need scarcely be added 
that it must be placed as far as possible away from bottles 
or other frangible articles, otherwise accidents are liable to 
occur by the forcible projection of fragments of crucibles, 
stones, &c. 

The cold chisel (fig. 4) is employed for cutting off me¬ 
tallic masses for assay. It should be five or six inches long, 
and about half an inch wide, which is the best size for 



general use. However, for some purposes, as cutting copper 
and other very tough metals, it is convenient to have a chisel 
only a quarter of an inch wide, as these metals are so much 
more difficult to cut, and the small chisel meets with the 
least resistance. 

Small shears (fig. 5) are also exceedingly useful in cutting 
off pieces of sheet metal, as lead, for cupellation, scorifica- 
tion, &c. 

The Pestle and Mortar. —Mortars are made of various 
materials, as cast-iron, bronze, porcelain, agate, &c. ; the 
assayer requires one of cast-iron, one of porcelain, and one 
of agate. 

The iron mortar (fig. 6) ought to be of the capacity of 


Fig. 6. 



from three to four pints ; the porcelain (Wedgwood ware) 












14 


USE OF PESTLE AND MORTAR. 


(fig. 7) may contain about two pints. The ease with which 
a mortar may be used, depends much upon its form ; and 
opinion is greatly divided on this subject. Faraday * says 
that the pestle should be strong, and the size of its superior 
part such as may be sufficient to allow of its being grasped 
firmly in the hand, and below to permit a considerable 
"rinding surface to come in contact with the mortar. Its 
diameter in the lower part may be about one-third or one- 
fourth of the upper diameter of the mortar. The curve at 
the bottom should be of shorter radius than the curve of 
the mortar, that it may not touch the mortar in more than 
one part, whilst at the same time the interval around may 
gradually increase, though not too rapidly, towards the 
upper part of the pestle. 

The bottoms of all mortars ought to be of considerable 
thickness, in order to withstand the smart blows they will 
occasionally have to receive. 

Berzelius recommended (and I have found it extremely 
serviceable) a mass of pumice-stone for cleansing porcelain 
mortars. It is used with water as a pestle, and in course of 
time will be worn to the shape of the mortar ; its action will 
then be more speedy. 

Iron mortars can be best cleaned by friction, with a little 
fine sharp sand, if the ordinary process of washing be not 
sufficient to remove the adhering substance. Great care 
must be taken to perfectly dry mortars, especially those of 
iron, otherwise they will become rusted, and the rust so 
formed will contaminate the substances pulverised in them. 

The iron mortar is principally of use in the reduction of 
the masses of mineral (broken on the anvil, as before de¬ 
scribed) to a state of coarse powder, in order to render the 
substance more readily capable of pulverisation, strictly so 
called. In the use of the iron mortar, all friction with the 
pestle ought to be avoided, and the body within it must be 
struck repeatedly and lightly, in a vertical direction, taking 
care to strike the large pieces, so that all may be equally re¬ 
duced. This can be carried on until the whole is about the 


* Chemical Manipulation, p. 141). 


15 


PULVERISATION OF TIIE SAMPLE. 


size of line sand ; it can then be transferred to the porce¬ 
lain mortar, where direct blows must be carefully avoided. 

The process is now thus carried on : the pestle is to be 
pressed upon with a moderate force, and a circular motion 
given to it, taking care every now and then to lessen and en¬ 
large the circles so as to pass over the whole grinding surface 
of the mortar, and ensure the pulverisation of the mass of 
mineral submitted to operation. In general, the finer the 
state of division to which a mineral is reduced, the more 
accurate and expeditious will be its assay ; and in preparing 
a mineral for assay by the humid method, no labour ought 
to be spared on this point. Pulverisation is rendered much 
easier by operating on a small quantity at once, and remov¬ 
ing it very often from the sides and bottom of the mortar by 
means of a spatula. The quantity operated on at one time 
must be regulated by the hardness or friability of the sub¬ 
stance whose pulverisation is to be effected. The harder it 
is, the less must be taken, and vice versa. 

In the use of the iron mortar fragments are occasionally 
projected. This may be prevented by covering the upper part 
of the mortar with a cloth. This applies also to the porcelain 
mortar, for the dust of some minerals has a disagreeable 
taste and smell. The operator may in some measure pro¬ 
tect himself by means of the cloth. Indeed, in some cases, the 
ambient powder is highly deleterious, as in the pulverisation 
of arsenical nickel, cobalt, and other ores. Here the simple 
cloth is not a sufficient protection ; it should be slightly 
damped with water, and tightly tied round the mortar, and 
firmly held round the pestle, when nothing can escape. 

Some minerals can be pulverised with greater ease if they 
are ignited and suddenly quenched in cold water. Amongst 
them may be named flint, and many other siliceous matters, 
as gold quartz. In the pulverisation of charcoal for assays, 
it will also be found advantageous to ignite it, as hot charcoal 
is more readily pulverised than cold. 

In some instances the powder obtained in the iron or 
porcelain mortar is not fine enough ; recourse should then 
be had to the agate mortar, in which the mineral, in as fine 
a state of division as the larger mortars will give it, is 


16 


STEEL CRUSHING MORTAR. 


ground in small portions at a time, until it is reduced to an 
impalpable powder. 

When small specimens or rare minerals are being operated 
upon, or if it is especially desirable to avoid loss, it is advisable 

to use a steel mortar (fig. 8) for 
the preparatory reduction of 
the mineral to coarse powder. 
A B and C I) represent the 
two component parts of the 
mortar; these may be readily 
taken asunder. The substance 
to be crushed (having, if prac¬ 
ticable, first been broken into 
small pieces) is placed in the 
cylindrical chamber <?, f ; the 
steel cylinder, which fits some¬ 
what loosely into the chamber, 
serveft as a pestle. The mortar 
is placed upon ji solid support, 
and perpendicular blows are repeatedly struck upon the 
pestle with a hammer, until the object in view is attained. 
( Fresenius .) 

In the selection of agate mortars, they must be examined 
to see that they have no palpable flaws in them ; very slight 
cracks, however, that cannot be felt, do not render the mor¬ 
tar useless, although they increase the danger of its destruc¬ 
tion bv a chance blow. 

V 

The Sieve —The operation of sifting is employed when a 
very fine powder is required, or when a powder of uniform 
size is needed. Sieves of various materials and different 
degrees of fineness are necessary. The larger sieve, for 
preparing coke for the blast furnace, is made of stout iron 
wire, and must have its meshes from 1 inch to inch 
square. The fine coke, which is sifted from that which is 
the proper size for the blast furnace, may be mixed with 
that of ordinary size, and employed economically in the 
muffle furnace. For the preparation of minerals, a set of 
three sieves should be provided, each one finer than the other. 
The coarsest may contain 40 holes to the linear inch, the 
finer or medium sieve GO, and the finest from 80 to 100. 







THE OPERATION OF SIFTING, 


17 


The coarsest sieve is used for preparing galena for assay ; 
the medium, for copper, tin, iron, and other like ores; and 
the finest, for gold and silver ores, or for preparing any sub¬ 
stance for the wet assay, as, in the latter case, the finer the 
state of division the substance attains, the more rapid will be 
its solution or decomposition by the liquid agents employed. 

The sieve fig. 9 is made of wood, over which is strained 
in the ordinary manner brass wire-gauze of the necessary 
degree of fineness. When in use, B , fig. 10, is fitted into 
the lower part of A (same figure). This contrivance pre¬ 
vents all loss of the fine powder. If the matter to be sifted 
be offensive or deleterious to the operator, a sieve termed 
the drum or box-sieve may be employed (see fig. 10), where 
C represents a cover fitting over the sieve. If small, this 
may be used in the ordinary way; but if large, its method 
of use is rather peculiar, and requires some practice to fully 
develop its powers. One side of the under edge must be 
held by one or both FlCr> 9 p IG . i 0 . 

hands, according to its 
size, whilst the other 
rests on a table or a 
bench. A semi-circu¬ 
lar oscillating motion 
must now be com¬ 
municated to it by 
moving the hands up 
and down at the same 
time they are being 
alternately brought 
into approximation with the sides of the operator. 

In cases of necessity, a sieve may be readily extemporised. 
Place the powder to be sifted in a piece of fine lawn, or 
muslin, according to the fineness required, tie it up loosely, 
and shake or tap the powder, with its muslin or other envelope, 
on a sheet of paper, and the sifting will be rapidly and 
easily accomplished. 

The sieve is also extremely serviceable in the separation 
of some ores from their gangues or vein-stones, especially 
if the latter be stony and hard. This point must be parti- 

c 














































18 


ELUTRIATION. 


cularly noted, as it is the cause of much variance between 
the results of different assayers ; for instance, part of the 
same sample of ore might be sent to two assayers, and the 
produce made by one would be 8.J, per cent., and that by 
the other 9 or 9^, or, in some cases, even more. This dis¬ 
crepancy generally arises from the cause above mentioned. 
In the one case, the workman has rejected part of the hard 
gangue, and so rendered the residue richer; whilst in the 
other he has pulverised the whole, making the produce less, 
but giving more accurately the amount of metal in the sub¬ 
stance submitted to assay. 

A knowledge of this fact is also very useful from another 
point of view ; suppose it were wished to separate in a 
speedy manner, as perfectly as possible, any friable mineral, 
such as galena or copper pyrites, from its matrix by me¬ 
chanical means ; it might be accomplished by the use of the 
sieve, as follows: Place a small quantity of the mineral in 
an iron mortar, and strike, repeatedly, slight vertical blows. 
When it is tolerably reduced, sift it, and it will be found that 
what passes through is nearly pure mineral, with only a 
small quantity of matrix; repeat the pounding and sifting 
operations, until, after a few repetitions, that which remains 
in the sieve is nearly pure gangue. 

Native metals, as gold, silver, and copper, are also par¬ 
tially separated after the manner above described. The fine 
particles of metal, during the process of pounding and 
trituration, become flattened, and refuse to pass through the 
sieve, whilst the more brittle portions pass through, and are 
separated. 

Elutriation. —This process can only be employed for 
those bodies which are not acted on by water; and it 
must be remembered that many substances which are 
usually considered to be insoluble in water, are, when in a 
very finely divided state, acted upon by this liquid to a 
more or less extent. The operation is thus effected : The 
substance is reduced to the finest possible state of division 
by any of the foregoing processes; it is then mixed with a 
quantity of water in a glass or other vessel. After a few 
moments’ repose, the supernatant liquid, retaining in sus- 


WASHING, DRESSING, OR VANNING. 


19 


pension the finer particles of the pulverised substance, is 
poured off, and the grosser parts, which have fallen to the 
bottom of the vessel, are re-pulverised, and again treated 
with water. By repeating these processes, a powder of 
any required degree of fineness may be obtained. 

It is seldom, however, that a substance is required for 
assay by the dry way, in such a minute state of division 
as is produced by this process. In the humid or wet 
method it is occasionally very useful. If the supernatant 
water is roughly decanted off, in certain cases, where 
the powder to be elutriated is light, the least disturbance of 
the vessel containing it occasions the distribution of the 
portion which has settled, throughout the liquid, and the 
consequent mixture of fine and coarse particles. This can 
be avoided by the employment of the syphon. The operation 
is then thus conducted: The syphon is filled with water, 
and the shorter end placed in the liquid whose transversion 
is to be effected; the forefinger of the right hand, which, 
during this time, has been applied to the longer end of the 
instrument, is now removed, when the water will flow out 
until it is level with the immersed end of the syphon. Fresh 
water can then be added, the powder stirred up again, and 
the operation of decantation by the syphon carried on as 
long as requisite. 

Washing, Dressing, or Vanning. —This operation is ex¬ 
ceedingly useful for discovering the approximate quantity 
of pure ore, such as galena, copper pyrites, oxide of tin, 
native gold or silver, in any sample of earthy matter or 
ore in which it may be disseminated. 

The theory of the operation about to be described is 
easily understood. Bodies left to the action of gravity in a 
liquid, in a state of rest, experience a resistance to their 
descent which is proportionate to their surface, whatever 
may be their volume and density. Hence it follows, firstly, 
that of equal volumes the heaviest fall most rapidly; secondly, 
that of equal densities those having the largest size move with 
the greatest speed ; for in particles of unequal size and like 
form the weight is proportional to the cube of the dimen¬ 
sions, whilst the surface is only proportional to the square of 


2o 


WASHING OR VANNING ORKS. 


these dimensions; lienee in small particles the surface is 
greater in relation to the weight than in the large particles; 
thirdly, that of equal densities and volumes, particles 
offering the largest surface (those which are scaly or 
laminated, for example) undergo more resistance in their 
motion than those which, approaching the spherical form, 
have less surface. The adhesion of the liquid to the 
particles of bodies held in suspension is also an obstacle to 
their subsidence. This force, like the dynamic resistance, 
is proportional to the surface and independent of the mass 
or volume, whence it follows that, in a fluid in motion, 
of bodies having equal volumes, the least dense acquire 
the greatest rapidity of movement, and are deposited at 
the greatest distance from the point of departure ; whilst 
with equal densities the smallest grains are carried farthest; 
and, lastly, with equal densities and volumes the particles 
exposing most surface traverse the greatest space. 

It is, therefore, evident that the most advantageous con¬ 
dition for separating, by washing, two substances of unequal 
specific gravity or density, is that the heavier shall be in 
larger grains than the lighter; this unfortunately, however, 
is a condition that can very seldom be fulfilled, as the 
heaviest substances are those metallic minerals whose fran- 
gibility is nearly always greater than the earthy matters 
accompanying them as gangues. This being the case, it is 
very important so to arrange that the fragments of the various 
mixed substances shall be nearly of the same size. This 
may be effected by very frequently sifting the mineral 
during the process of pulverisation, reducing it also more 
by blows than by grinding, so as to get as little fine powder 
as possible, as that is nearly certain to be washed away 
during the process. 

The operation of washing or vanning may be performed 
by one of two methods. In the first, a small stream of 
running water is employed; in the second, water is added 
to the substance to be washed, and poured off as necessary. 

In the first process, a vessel somewhat resembling a 
banker’s gold scoop (but longer in proportion) is employed; 
the mineral to be washed is placed in the upper part, and a 


WASHING OR VANNING ORES. 


21 


small quantity of water added, with which the mineral is 
thoroughly and carefully moistened, and mixed with the 
lingers. The scoop must then be so inclined that a fine 
stream of water from any convenient source (say a tap) may 
fall just above the upper part of the mixture of mineral and 
water; then, firmly holding the larger and upper end 
of the scoop with the left hand, and sustaining the lower 
part with the right, it is shaken frequently in the direction 
of its longitudinal axis. At each shake, all the particles 
in the scoop are so agitated that they become suspended 
in the water, and the current of liquid running from the tap 
into the scoop moves them all in its own direction; but they 
are deposited at different distances from the point at which 
the water enters, the heaviest being carried through but a 
very small space. It is now soon seen that the mineral 
assumes a heterogeneous surface; at the upper part, the 
heavy portions are seen nearly pure ; the light substances, 
on the other hand, are nearly without mixture at the lower 
end, and in the intermediate part the heaviest portion of the 
mixture is nearest the upper end. If the washed matter 
were now to be divided into horizontal layers, the heaviest 
matter would be found at the bottom, and the lightest on 
the surface. Things being in this state, the scoop must be 
made to oscillate on its axis, so that the latter remain 
immovable, and in a slightly inclined position. In this 
manner, the layer of water running over the surface of the 
mineral agitates that part only, and carries off all light sub¬ 
stances there deposited in the previous operation. When 
necessary, these matters may be removed by the finger, and 
made to run into a vessel placed below the scoop, in which 
all the water and matters carried off are received. This 
operation, however, must not be hurriedly performed, so as 
to mix the parts already separated: each layer must be re¬ 
moved separately, commencing with the upper one. This 
being done, the scoop must be alternately kept in motion by 
shakings, as at first, and then on its axis, and the washing 
off of the finer particles renewed, and so on until the separa¬ 
tion is effected as far as may be judged necessary. 

At the commencement of the operation, the water carries 


22 


WASHING AND VANNING. 


out of the scoop the lightest particles,' as organic matter, 
clay, &c.; at a little later period the water carries with it 
a small but definite quantity of the heavier portion, the 
proportion of which increases as the operation proceeds, 
until at last the greatest possible care is required. It is 
always better to rewash the latter portion which passes off 
from the scoop ; hence the necessity of allowing all the wash- 
water passing from it to collect in a vessel placed for that 
purpose. 

In the second method of washing, a tin, zinc, or wooden 
pan is employed. It should be circular, one or two feet in 
diameter and three or four inches deep; the sides should 
descend in a conical manner, so that the bottom is not more 
than four inches in diameter, and the angle between it and 
the sides as sharp as possible. 

The substance to be examined is placed in the wasliing- 
dish, the latter filled with water, and the mineral well mixed 
with it until perfectly moistened, as before. After a moment 
or so the muddy water is poured off, and the operation 
repeated until the water passes off clear. When this 
happens, only so much water must be placed in the pan as 
will leave a slight layer on the mineral. Now, by holding 
the pan in one hand, and shaking it with the other, the 
greater part of the heavy mineral, gold or otherwise, will fall 
below the sand. If now the pan be inclined towards the 
hand which is shaking it, the lighter portions, even if toler¬ 
ably large, will flow off with the water, leaving the heavier 
matters in the angle, from which, with ordinary care and a 
little practice, it is difficult to disturb them. If there be a 
large quantity of earthy matter, this may be (after sufficient 
shaking) removed by the finger, as in the first described 
process. By careful repetitions of these processes, the whole, 
or nearly the whole, of the sandy and earthy matters may be 
removed, and the gold or other mineral left nearly pure. 
This is the plan employed in prospecting for gold, diamonds, 
and other gems, and, in some cases, for their commercial 
extraction. 

In Cornwall, and other mining counties, this operation is 
very cleverly and carefully performed on the miner’s common 


OPERATION OF WEIGHING. 


23 


shovel, and the richness of any particular sample of either 
tin, lead, or copper is thereby determined with a very near 
approach to accuracy. 


THE BALANCE. 

Operation of Weighing. —At least three balances will be 
required in a laboratory where general assays are performed. 
The first must be capable of carrying three or four pounds in 
each pan, and must turn with a quarter of a grain. This 
may be of the form of the bankers’ or bullion balance (fig. 
11), and may be employed in weighing samples of gold 
quartz or silver ore containing metallic grains capable of being 


Fig. 11. 



separated by the sieve (see p. 18); the second (fig. 12), or 
rough assay balance, is similar to the apothecary’s scales; it 
should take 1000 grains in each pan, and turn with one-tenth 
of a grain. This serves for weighing samples of ore and fluxes 
for assay, and for determining the weight of buttons or prills 
of lead, tin, iron, copper, &c. obtained in an assay. 









•24 



TJIE BALANCE. 


The third and most delicate, or true assay balance (lig. 13) 
should carry about 1000 grains ; must turn distinctly and 


Fig. 12. 



accurately with the yoVo^ 1 °f a grain- This is employed in 
the assay of gold and silver bullion, and in the assay 


Fig. 13. 




























THEORY OF TJ1E BALANCE. 


25 


ot minerals containing gold and silver; also for general 
analytical purposes. The first two balances may be used, 
with ordinary care, by anyone ; but the third balance, in its 
use and adjustment so as to maintain its extreme accuracy, 
requires some particular instructions, which necessarily 
involve the principle of the balance. These have been so 
admirably given by Mr. Faraday, in his ‘ Chemical Manipu¬ 
lations,’ that we can do no better than transcribe them. 

4 The theory of this balance is so simple that the tests of 
its accuracy will be easily understood and as easily prac¬ 
tised. It may be considered as a uniform indexible lever, 
supported horizontally at the centre of gravity, and support¬ 
ing weights at equal distances from the centre by points in 
the same horizontal line with the centre of gravity. If the 
weights be equal the one will counterpoise the other ; if not 
the heavier will preponderate. In the balance, as usually 
constructed, there are certain departures from the theory as 
above expressed—some from the impossibility of execution, 
and others in consequence of their practical utility; and a 
good balance may be said to consist essentially of a beam 
made as light as is consistent with that inflexibility which it 
ought to possess, divided into two arms of equal weight and 
length by a line of support or axis, and also terminated at 
the end of each arm by a line of support, or axis, intended 
to sustain the pans. These three lines of support should be 
exactly parallel to each other in the same horizontal plane, 
and correctly perpendicular to the length of the beam ; 
and the plane in which the line should be raised more or 
less above the centre of gravity of the beam, so that the latter 
should be exactly under the middle line of suspension. It 
will be unnecessary in this place to speak of the coarse faults 
which occur in the ordinary scales—these will be easily un¬ 
derstood ; and from what has to be stated of the examination 
of the most delicate instrument, the impossibility of avoid¬ 
ing them without incurring an expense inconsistent with 
their ordinary use will be as readily comprehended.’ 

Two principal tilings have to be attended to in the selec¬ 
tion of a balance—its accuracy and its delicacy . The accu¬ 
racy depends upon the following conditions. 



26 


THEORY OF THE BALANCE. 

1. The arms should he equal to each other in length. The 
length of each is accurately the distance from the middle to 
the distant knife edge, all the edges being considered 
parallel to each other, and in the same plane. The two 
arms should accord perfectly in this respect. This equality 
may be ascertained in two or three ways. Suppose the 
balance with its pans to vibrate freely, and rest in a hori¬ 
zontal position, and that after changing the pans from one 
end to the other, the balance again takes its horizontal state 
of rest; in such a case, an almost certain proof is obtained 
of equality in length of the arms. They may, however, be 
equal, and yet this change of the pans from end to end may 
occasion a disturbance of equilibrium, because of the unequal 
distribution of weight on the beam and pans ; but to insure 
an accurate test, restore the pans, and consequently the 
equilibrium, to the first state: put equal, or at least counter¬ 
poising weights into the pans, loading the balance moderately, 
and then change the weights from one pan to the other, 
and again observe whether the equilibrium is maintained ; 
if so, the length of the arms is equal. 

Equality of weight is not so necessary a condition, 
although this should be obtained as accurately as possible. 
One arm with its pan may be considerably heavier than the 
other, but from the disposition of the weight in the lighter 
arm towards the extremity, or in the heavier towards the 
middle of the beam, the equilibrium may be perfect, and 
therefore no inaccuracy be caused thereby in the use of the 
balance. Instruments are usually sent home in equilibrium, 
and require no further examination as to this particular 
point than to ascertain that they really are in adjustment, and 
that after vibrating freely they take a horizontal position. 

2. The beam must be of such a form and strength that it 
will not bend when loaded with the greatest weight the balance 
is intended to carry. All well-made modern balances are 
sufficiently rigid in this respect, and may be safely trusted 
to carry their full weight without flexure of the beam. It 
should also be as light as practicable. 

3. The knife edges supporting the pans, ancl the centre one on 
which the beam vibrates , must be accurately in the same line. 


THEORY OF THE BALANCE. 


27 


The delicacy of a balance likewise depends upon several 
conditions. 

The centre of gravity must be very little below the fulcrum. 
If it be considerably depressed, then, upon trying the oscilla¬ 
tions of the balance by giving it a little motion, they will 
be found to be quick, and the beam will soon take its 
ultimate state of rest ; and if weights be added to one side, 
so as to make it vibrate, or to bring it to a certain per¬ 
manent state of inclination, the quantity required will be 
found to be comparatively considerable. As the centre of 
gravity is raised the oscillations are slower, but producible 
by a much smaller impulse; the beam is a longer time 
before it attains a state of rest, and it turns with a smaller 
quantity. 

If, however, the centre of gravity coincides with the 
fulcrum or centre of oscillation, then the balance is said to 
set, that is, the smallest possible weight will turn the beam ; 
the oscillations no longer exist, but one side or the other 
preponderates with the slightest force, and the valuable 
indication which is furnished by the extent and velocity of 
the vibrations is lost. 

The case in which the centre of gravity is above the 
fulcrum rarely if ever occurs. Such a balance, when equally 
weighted, would set on the one side or the other, that side 
which was in the slightest degree lower tending to descend 
still further, until obstructed by interposing obstacles. 

In balances intended to carry large quantities (as in the 
balance for weighing gold quartz, &c.) it is necessary to 
place the centre of gravity lower than in those for minute 
quantities, that they may vibrate regularly and readily. 
This is one cause why they are inferior in delicacy, for, as a 
consequence of the arrangement, they will not turn except 
with a lamer weight. 

Balances are also liable to set when overloaded. Thus, 
if a balance be equally weighted in each pan, but overloaded, 
it will, if placed exactly horizontal, remain so, but the 
slightest impulse or depression on one side destroys the 
equilibrium; the lower side continues to descend with an 
accelerated force, and ultimately remains down, being to all 


28 


THEORY OF THE BALANCE. 

appearance heavier than the other. Generally speaking, 
the more delicate a balance the sooner this effect takes 
place ; this is one limit to the weight it can properly carry. 

The vibrations of a balance vary with the quantity ol 
matter with which it is loaded: the more the weight in 
the pans, the slower the vibration. These should be ob¬ 
served, and the appearances retained in the mind, in con¬ 
sequence of the useful indications they afford in weighing. 
A certain amplitude and velocity of vibration would indi¬ 
cate to a person used to the instrument, nearly the weight 
required to produce equilibrium; but the same extent and 
velocity, with a weight much larger or smaller, would not 
be occasioned by an equal deficiency or redundancy of 
weight, as in the former case. 

The weight also required to effect a certain inclination oi 
the beam, or to turn it, should be known, both when it is 
slightly and when it is heavily loaded. Thus, if the instru¬ 
ment turns with yornyth of a grain, with 1000 grains in each 
pan, or with y<y o o^ 1 °f ^ ie weight it carries, it may be 
considered perfect. 

The friction of the knife edges must be as slight as possible. 

Most of the faults in the working of a balance, if ordi¬ 
narily well made, depend upon imperfections in the middle 
knife edge and the planes upon which it rests. 

The edge is made either of agate or steel, preferably the 
former, and should be formed out of one piece, and finished 
at once, every part of the edge being ground on the same 
flat surface at the same time. In this way the existence of 
the two extreme or bearing parts of the edge in one line is 
insured ; but when the two parts which bear upon the planes 
are formed separately on the different ends of a piece of 
agate or steel, or, what is worse, when they are formed on 
separate pieces, and then fixed one on each side the beam, 
it is scarcely possible they should be in the same line ; and 
if not, the beam cannot be correct. These knife edo-es 
usually rest on planes, or else in curves. The planes should 
be perfectly fiat and horizontal, and exactly at the same 
height; the curves should be of equal height, and their axes 
in the same line. If they are so, and the knife edge is 


•29 


TESTING THE ACCURACY OF A BALANCE. 

perfect, then the suspension will be accurately on the line 
ot the edge, and reversing the beam will produce no change. 
The balance must always be kept perfectly level by means 
of the three screws on which it stands, and adjusted by the 
spirit-level or plumb-line with which it is furnished. 

The balance should be kept in a well-lighted dry room, 
quite away from acid or other vapours. The case should be 
kept closed as much as possible, and a glass vessel full of 
lumps of good quick-lime should be kept in it. When the 
lime falls to powder it should be renewed. 

In order to test the accuracy and delicacy of a balance, 
remove the pans and their end supports, and notice how the 
beam oscillates. When it has been found to oscillate with 
regularity, and gradually to attain a horizontal position of 
rest, it should be reversed—that is, taken up and turned 
half-way round, so as to make that which before pointed to 
the right now point to the left. The beam should then 
again be made to oscillate, and if it perform regularly as 
before, finally resting in a horizontal position, it has stood 
a severe test, and promises well. Then replace the pans and 
repeat the tests, noticing the time required for each oscillation. 
When the pans are hung upon the beam, the balance should 
of course remain horizontal. They should be tried by chang¬ 
ing then by reversing the beam, and afterwards by changing 
the pans again. The pans are best suspended by very thin 
platinum wire, so as to avoid hygrometrical influence upon 
them. 

Afterwards load the balance with the full weight it is 
intended to carry—say 1000 grains in each pan, and notice 
if the indications are as rapid upon adding or subtracting the 
smallest weight as they were when the pans were empty. 

Tests of this kind are quite sufficient for the purpose of 
the assayer, who, having ascertained that his balance, whether 
slightly or fully laden, vibrates freely, turns delicately, has 
not its indications altered by reversing the beam or changing 
counterpoising weights, may be perfectly satisfied with it. 

The irregularities which may be discovered by these tests 
are best corrected by a workman ; but as in all the best 
balances now made adjusting screws for these purposes are 



30 


WEIGHTS. 


provided, it has been thought advisable to introduce here 
such matter as, after careful perusal, will enable every one 
to adjust and examine his balance properly ; so that, in the 
absence of a skilled workman, it may without much danger 
be put into working order by the assayer himself, if acci¬ 
dentally damaged by rough treatment. 

The Weights. —Various kinds of weights are necessary for 
the different balances required by the assayer. For the larger 
balance, Troy-weights from 4 lbs. to \ grain will be re¬ 
quisite; for the second size, weights from 1000 grains to 
ytjth part of a grain ; and for the assay balance, weights from 

1000 grains to xoV o^ 1 °f a g ra i n - 

The best material adapted for weights is unquestionably 
platinum.. This is, however, too expensive for its general 
adoption, and therefore brass weights are almost invariably 
employed down to the ten or twenty grain weight, the 
smaller ones only being of platinum. On the Continent 
weights are generally made of silver, and if of brass are 
electro-gilt. For the smallest weights of all, those below 
0T0 grain, aluminium is often used, its lightness, and con¬ 
sequently greater bulk, enabling these small weights to be 
made considerably larger than if they were of platinum. 
The riders are generally of silver-gilt wire. The slight 
tarnish which gradually forms on brass weights may be 
disregarded until it becomes very thick. Weights ought 
never to be touched with the fingers, and should, when 
not in use, be kept tightly fastened in their box, away 
from all acid fumes. The most convenient series in which 
to have the weights is 600, 300, 200, 100, 60, 30, 20, 10, 
6, 3, 2, 1, -6, -3, *2, T, &c. This is preferable to the series 
formerly employed, as it admits of the use of a less number 
of weights to arrive at any required amount. 

Peculiar weights are necessary for the assay of gold and 
silver bullion in England (with the exception of assays for 
the Bank of England ; see Gold assay), gold being reported 
in carats, grains and eights, and silver in ozs. and dwts. The 
most convenient quantity of either of the precious metals for 
assay is 12 grains. The quantity taken, however, is of no 
very great consequence ; but whatever its real weight, it is de- 



ASSAY WEIGHTS FOR SILVER AND GOLD. 


31 


nominated in England the assay 4 pound .’ This assay 4 pound ’ 
is then subdivided into aliquot parts, but differing according 
to the metal. The silver assay 4 pound ’ is subdivided, as the 
real Troy pound, into 12 ounces, each ounce into 20 penny¬ 
weights, and these again into halves (the lowest report for 
silver), so that there are 480 different reports for silver, and 
therefore each nominal half-pennyweight weighs ^th part 
of a Troy grain, when the 4 pound ’ is 12 grains. 





Assay Weights for Silver. 


Silver 






Assay 

ozs. 

dwts. gra. 





grains 

12 

0 

0 





. 12 

11 

0 

0 





. 11 

6 

0 

0 





. 6 

3 

0 

0 





. 3 

2 

0 

0 





. 2 

1 

0 

0 





. 1 

0 

10 

0 





. 0-500 

0 

5 

0 





. 0250 

0 

3 

0 





. 0-150 

0 

2 

0 





. 0-100 

0 

1 

0 





. 0-050 

0 

0 12 





. 0025 


The gold assay 4 pound ’ is subdivided into 24 carats, each 
carat into 4 assay grains, and each grain into eights, so 
that there are 768 reports for gold, and the assay 4 pound’ 
weighing 12 Troy grains, the lowest report,or |4h assay grain, 
equals ^ ¥ th Troy grain ; thus 


Assay TVeights for Gold. 



Gold 







Assay 

carats grs. eights 






grains 

24 

0 

0 






. 12 

22 

0 

0 






. 11 

12 

0 

0 






. G 

6 

0 

0 






. 3 

3 

0 

0 






• lffthB 

2 

0 

0 






1 

1 

0 

0 






fftlis 

0 

2 

0 






£fths 

0 

1 

0 






• inrths 

0 

0 

6 







0 

0 

3 







0 

0 

2 






-fa ths 

0 

0 

1 




• 




In cases where the very smallest weights have to be em¬ 
ployed, great care must be taken in seizing them with the 
forceps, as they are apt to spring away and be lost. In the 
















32 


METHOD OF WEIGHING. 


assay balance (fig. 13), the use of weights less than 1 1 ^th of a 
grain is avoided by a very ingenious contrivance. Each side 
of the beam is equally divided into ten parts, and over the 
beam on either side is placed a sliding rod, as represented in 
the figure. The object of these rods is to carry, in the 
direction of the beam, the small bent piece of wire, (letter c, 
fig. 13,) called a rider , which serves in lieu of the smallest 
weights—the yJ^th anc ^ the ToVoth. These riders are thus 
employed : one weighing ^th of a grain is placed on the 
cross-piece of the extremity of the sliding rod just mentioned, 
and the rod thus furnished is brought gradually along the 
beam from the centre to the end, until the rider can be 
deposited on the division on the beam marked 10; the 
balance is then loaded on that side with a weight equal to 
yYyth of a grain. If now the rod be advanced to the centre 
of the balance, and the rider dropped on the mark 5, the 
half of T \yth of a grain will be pressing on that side of the 
balance, or, in other words, *05th of a grain ; and when the 
rider is at the marks 1,2, 3, 4, respectively, *01, *02, *03, -04 
of a grain will be indicated. With a rider weighing T t (( th 
of a grain, thousandths of grains may be indicated ; thus the 
last rider placed on the marks 1, 2, 3, 4, would equal *001, 
*002, *003, *004 grain, &c. 

The Method of Weighing.— The operation of weighing is 
very simple ; but as in the hands of the chemist and assayer 
it becomes one of great frequency, the facilities for its per¬ 
formance require to be mentioned. It should in the first 
place be ascertained before every operation that the balance 
is in order, so far as relates to its freedom of vibration, 
and also that no currents of air are passing through the 
case, so as to affect its state of motion or rest, a situation 
being chosen where such influence may be avoided. In 
most cases there is a small projecting arm on the upper part 
of the beam, which, being turned either to the right or 
left hand side of the beam, as required, serves to establish 
perfect equilibrium. Perfect equilibrium is, however, a 
matter of no consequence if the assayer observes one or 
two simple rules. He should never on any account weiqli 
by the direct method; that is, he should never obtain the 






OPERATION OF WEIGHING. 


33 


weight of a substance by putting it at once into one pan, 
and then counterpoising it by adding weights to the other 
pan. This method is only to be relied on when the balance 
is of rare perfection, and is used by no one but the assayer 
himself. The plan of weighing by difference should inva¬ 
riably be adopted. By this means the weight of any body 
can be readily ascertained, no matter whether the arms of 
the balance are of equal length or the pans are in equili¬ 
brium. 

In the first place, it should be a rule that one pan, pre¬ 
ferably the left, be reserved for the substance to be weighed, 
and the other pan be set apart for the weights. 

Supposing the weight of a portion of mineral is required. 
First place a clean watch glass, or platinum capsule, in the 
left pan, and carefully ascertain its weight. Let us suppose 
it weighs 106-347 grains ; now put the mineral in the watch- 
glass and ascertain the united weight of the two. This we 
will imagine comes to 763*776. By subtracting the weight 
of the glass or capsule from this we find the true weight of 
the mineral, which is 763*776 -106-347 = 657-429. The 
substance to be weighed must never be put direct into the 
pan. By weighing in this manner by difference the errors 
arising from inequality in the equilibrium or length of arms 
are eliminated. 

Nothing should ever be weighed until it is perfectly cold. 
It is also inadvisable to weigh anything immediately after 
it is taken from a cold place to a warmer one, as the 
substance in such case will act as a hygroscopic body, and 
by condensing moisture, will appear heavier than it really is. 

Powders are conveniently weighed by filling a small 
stoppered tube bottle with them, then weighing the whole, 
and after pouring out the requisite amount of its contents, 
re-weighing the bottle and powder. The difference gives the 
weight of powder used. This is a very convenient plan if 
several portions of the same substance are required for 
different analyses. The tube will require re-weighing each 
time after the quantities required for each analysis are 
shaken out into the receptacles. 

A delicate balance is always furnished with means of 

D 


34 


OPERATION OF WEIGHING. 


supporting the pans independent of the beam ; and the 
beam itself is also supported when required by other bear¬ 
ings than its knife edges, and in such a manner as to admit 
of the rapid removal of these extra supports, that the 
instrument may be left free for vibration. This is done that 
the delicate edges of suspension may not be injured by 
being constantly subjected to the weight of the beam and the 
pans, and that they may suffer no sudden injury from undue 
violence or force impressed upon any part of the balance. 
When, therefore, a large weight of any kind is put into or 
removed from the pans, it should never be done without 
previously supporting them by these contrivances ; for the 
weight, if dropped in, descends with a force highly injurious 
to the supporting edges ; also if a large weight be taken out 
without first bringing the pans to rest, it cannot be done 
without producing a similarly bad effect. 

The weights should not be put into the pan at random. 
11 is a mistake to suppose that time is saved by such a plan. 
The highest probable weight should be added first, and then 
the set should be gone through systematically down to 
the smallest weight, retaining or removing each weight in 
order according as it is too little or too much. The exact 
weight of a body will be found in this manner in far less 
time than would be required were the weights added by 
guess. 

When a weight is put in which is assumed to be nearly 
equal to the substance to be weighed, the balance should 
be brought to a state of rest, and should then be liberated 
gradually by turning the handle, so as to leave the pans 
wholly supported by the beam. The whole being on 
its true centres of suspension, it will be observed whether 
the weight is sufficient or not; and the rapidity of ascent 
or descent of the pan containing it, will enable a judg¬ 
ment to be formed of the quantity still to be added or 
removed. 

Great care should be observed in recording the weight in 
the note-book. The weight should first be ascertained from 
an inspection of the vacancies in the box of weights, and 


WEIGHING MOIST PRECIPITATES. 


/ 


35 


then verified by an examination of the weights themselves. 
This is conveniently done whilst replacing them in the box, 
which slionld be done immediately after each weighing. 

In some cases, where great accuracy is not of so much 
importance as rapidity in getting out approximate results, a 
plan may be adopted recommended by Mr. F. F. Mayer in 
the American 4 Journal of Science and Art ’ for 1861. 

Mr. Ch. Mene, of Creusot, gave (in the Journ. de Pharm. 
et de Chimie, for October, 1858) a mode of weighing which 
does away to a great extent with the tediousness and dif¬ 
ficulties attending the drying of many precipitates. He 
washes the precipitate thoroughly by decantation, and then 
introduces it carefully into a bottle the exact weight of 
which when filled with distilled water at a certain tem¬ 
perature is known. Since the precipitate is heavier than 
water, the bottle when filled again will weigh more than 
without the precipitate, and the difference between the 
two weights furnishes the means of calculating the weight 
of the precipitate. 

In case the precipitate settles but slowly, it may be col¬ 
lected on a filter, and, together with a filter, after washing, 
be introduced into the bottle, in which case the weight of 
the filter and its specific gravity, supposing any difference 
should exist between its own and that of water, is to be 
taken in account. Precipitates soluble in or affected by 
water may be weighed in some other liquid. 

Mr. Mayer has applied this principle on a large scale as 
far back as 1855. 

In that year he was engaged in the manufacture of car¬ 
bonate of lead from refuse sulphate of lead, by treating the 
latter, in a pulpy condition, with carbonate of soda. The 
sulphate of lead used contained very varying proportions of 
water and soluble impurities; from which latter it had first 
to be freed by washing. It was then in the state of a thin 
pulp, and the difficulty was to find the amount of the dry 
sulphate of lead, as it was a matter of importance to use a 
little carbonate of soda, and to obtain as pure a carbonate 
of lead and sulphate of soda as possible. This could only 
be done by weighing it as whole or in portions; but as the 

D 2 



3G 


WEIGHING MOIST PRECIPITATES. 


drying of a tubful of sulphate of lead (from 500 to 1 200 lbs.) 
was impracticable, and sampling not less so, since the upper 
strata contained a much larger proportion of water than the 
lead at the bottom, the following method was contrived, 
which enabled the management of the process to be left in 
the hands of a workman — 

A strong oaken pail was taken, weighing 8 lbs. when empty, 
and a black mark was burnt in horizontally around the 
inside of the pail two inches below the rim, up to which 
mark it held 20 lbs. of water. The specific gravity of 
sulphate of lead being 6*3, the pail, if filled up to the mark, 
would hold 126 lbs. of pure sulphate of lead. The specific 
gravity of water being 5*3 less than that of sulphate of lead, it 
followed that if there were 1 lb. of water in the pailful of 
moist sulphate, the pail would weigh 5*3 lbs. less than 126 
(+ 8, the tare of the pail)=120*7( + 8); if there were 2 lbs. 
of water present, the weight would be 115*4( + 8), and so 
on. This enabled a table to be calculated giving in one 
column the actual weight of the pail when filled with moist 
sulphate, and opposite, in a second column, the amount of 
dry sulphate corresponding to the gross weight. The weight 
of dry sulphate was thus found as accurately as could be 
desired, although the amounts varied in practice from 30 to 
105 lbs. 

This is nothing but an application of the Archimedean 
theorem, that when a solid body is immersed in a liquid, it 
loses a portion of its weight, equal to the weight of the 
fluid which it displaces or to the weight of its own bulk of 
the liquid. 

This is precisely the principle applied by Mr. Mene. The 
precipitate he obtains by a certain chemical manipulation, is 
a substance of known composition and specific gravity. 
Supposing it to be sulphate of lead, and the bottle when 
fdled with water at the normal temperature to weigh 70 
grammes = 50 grammes of water and 20 for tare. After 
introducing the precipitate and filling again with water 
it weighs 71-06 grammes. Now as the specific gravity of 
sulphate of lead is 6*3, or as the weight of a cubic measure 
of sulphate of lead is 6*3 times that of a cubic measure of 



WEIGHING MOIST PRECIPITATES. 


37 


water, and as the space of one part by weight of water is 
taken up by 6’2 parts by weight of sulphate of lead, it 
follows that the quantity of the sulphate of lead in the 
bottle, which has taken up the space of one part by weight 
of water, increases the original weight of the bottle (filled 
with pure water) by 5 3. To find the amount of water 
displaced it is only necessary to divide the overweight (1 06 
grammes) by 5*3 = 0*2, which added to the overweight T06 
■+ 0*2 gives T26 grammes as the weight of the precipitate. 

Hence the rule, which is of great convenience in volu¬ 
metric analysis, that to find the weight of a moist precipitate 
which is a compound of known specific gravity, weigh it in a 
specific gravity bottle or some other vessel of known weight 
when filled with water, or any other liquid at the normal 
temperature; again fill it with the water or other liquid, 
divide the excess of the new weight by the specific gravity 
of the substance, less that of the water or other liquid (that 
of water being =1), and add the quotient to the overweight, 
which gives the weight of the precipitate. 

The principle exemplified by Mr. Mayer may not be 
novel; but as it has never been fully exemplified before, 
chemists and assayers, as well as manufacturers, especially of 
colours, will probably also find it of interest, and certainly 
highly practicable and easy of execution. 


38 


CHAPTER III. 

GENERAL PREPARATORY CHEMICAL OPERATIONS. 

Calcination.— Strictly speaking the term calcination means 
the production of an oxide or calx by combustion, and it 
necessarily involves the intervention of atmospheric oxygen. 
But in a metallurgical sense the term is restricted to the 
separation of any volatile matter from a mineral substance by 
the aid of heat alone, the atmosphere being totally or par¬ 
tially excluded, or the production of rapid changes of 
temperature, so as, for instance, to render minerals more 
fragile by quenching in water, &e. 

Tiius, we speak of the calcination of minerals, as iron, or zinc, 
ores, &c., whose matrices are argillaceous, to expel water; 
and also of gypsum to expel water ; the carbonates of lime, 
iron, copper and lead, are calcined to separate carbonic acid ; 
the hydro-carbonates of zinc and iron, to get rid of both 
water and carbonic acid ; cobalt, nickel ores, &c. to separate - 
arsenic and sulphur ; the iron ore found in the vicinity of 
collieries, to expel bituminous matter; and wood and bones 
to expel volatile organic matter. Where the operation is 
accompanied by combustion, and requires the oxygen of the 
atmosphere, it is termed roasting. 

Crucibles are conveniently used in calcination, as no stir¬ 
ring of the mass is required. They may be made of various 
materials, as clay, plumbago, platinum, silver and iron. 
Silver cannot be employed at a heat greater than dull 
redness. The selection of the crucible must depend upon 
the substance under operation ; they must all be furnished 
with covers. 

In almost all operations m assaying it is necessary to 
estimate the amount of volatile matter lost by calcination. 

A very high temperature is seldom required in calcination ; 



CALCINATION. 


39 


usually an air furnace will give enough heat. When the 
operation is finished, the crucible must be removed from the 
fire and allowed to cool gradually. When completely cold, 
remove the cover and take out the contents by means of a 
spatula. If any adhere, a small brush will be found very 
useful for its removal. The difference in weight before and 
after calcination will represent the volatile matter. 

When the substance to be calcined is fusible, the crucible 
and contents must be weighed before ignition ; and the loss 
of weight is equal to the quantity of volatile matter expelled ; 
in fact, this latter is usually the most satisfactory method 
of conducting the experiment. 

If the ignited or calcined substance be soluble in water, 
it can be removed from the crucible by that menstruum, 
employing heat if required ; if not, any suitable acid may be 
used. 

If the substance to be calcined decrepitates on heating, it 
must be previously pulverised and heated slowly and gradually 
in a well-covered crucible. 

Certain substances, as carbonate of lead, undergo a material 
alteration by contact with the gases given off during the 
combustion of the fuel in the heating furnace ; others, such as 
carbonaceous matters, are consumed by the introduction of 
atmospheric air. All such substances must be calcined in a 
closely-covered crucible placed in a second crucible (also 
covered) for further protection. 

In some rare cases, however, these precautions are not 
sufficient. In such, either a weighed porcelain or German 
glass retort must be employed. 

Sometimes earthenware crucibles lined with charcoal are 
employed in calcination; for even if the substance be 
fusible it may generally be collected and weighed with¬ 
out loss, as very few bodies either penetrate into or 
adhere to a charcoal lining. In this way grey cobalt and 
other arsenio-sulphides are calcined at a high tempera¬ 
ture to expel the greatest possible amount of arsenic and 
sulphur. 

The selection and proper management of crucibles will 
be given in the next chapter. 


40 


ROASTING ORKS. 


Roasting. —In this operation carbon, sulphur, selenium, 
antimony and arsenic are separated from certain metals with 
which they were combined. Roasting differs from calcination 
in this particular, the latter is carried on in close vessels, 
independent of the atmosphere, the former in open vessels 
by the aid of the atmosphere. It is thus we are enabled to 
separate the bodies just mentioned by this process; for the 
oxygen of the air, by combining with them, forms a volatile 
substance which the heat expels. Thus, in roasting sulphide 
of copper and iron (copper pyrites), the sulphur, copper, and 
iron mutually combine with oxygen to form sulphurous acid 
(volatile), protoxide of copper and peroxide of iron, thus :— 

2(FeS + CuS) + 130 = Fe 2 0 3 + 2(CuO) + 4(S0 2 ). 

This is the final change in this case. During the process, 
however, some sulphate and sub-sulphate of copper and iron 
are formed. This change will be given under the head of 
Copper Assay. 

When carbonaceous matters are roasted, the operation 
also takes the name combustion , or incineration ; because the 
object of roasting a fuel, for instance, is generally to ascertain 
the amount of ash left. 

In roasting, in the ordinary acceptation of the term, the 
body must not be fused, but kept in a pulverulent state; but 
there are some cases in which fusion is allowable, as in appel¬ 
lation and scorification. 

The process of roasting is performed in different ways; in 
one, a small fiat vessel, called a roasting test (fig. 14) is em¬ 
ployed, made of the same material as the earthen crucibles, 
and similar to a saucer. It is most conveniently heated in a 
muffle. The substance to be roasted must be finely pul¬ 
verised, placed in the roasting vessel, and constantly stirred 
with an iron or glass rod until no fumes are given off, or 
until it ceases to evolve the odour of sulphurous acid, when 
sulphur is one of the constituents to be eliminated. 

The operation may also be performed in a crucible, in which 
case it must be inclined to the operator, so that the draught 
of air passing to the furnace flue may impinge as much as 
possible on the substance under manipulation. 



41 


ROASTING OltKS. 

During roasting the heat must be earefifflr fCguTated for 
some time. At first it ought only to be the dullest red ; 
and the substance must be assiduously stirred in order to 
present the largest possible surface to the action of the 
atmosphere, and prevent fusion, for some assays, when 
roasting, will fuse readily at a low temperature unless the 
surface be continually renewed. Even by paying the ut- 


Fig. 14. 



most attention to this point it cannot be always prevented, 
as for instance when sulphide of antimony is being roasted. 
In these cases the assay must be mixed with its own weight 
of powdered quartz or fine white sand (silver sand) : the 
operation will then proceed steadily. 

If the assay at all agglutinates it must be taken from the 
fire, and rejected if the substance be plentiful; if not, the 
fused mass must be carefully removed from the crucible or 
test, pulverised, and the roasting recommenced. In this 
case, however, the operation is always very tedious, and the 
final result less exact, so that great care ought to be taken 
at the commencement of the roasting. 

When the assay has been kept at a dull red heat for some 
time, and shows no signs of agglutination, the heat may be 
slightly increased; at the same time stirring must be dili¬ 
gently pursued. After the heat has arrived at full redness 
there is little fear of fusion; and as the operation proceeds 
more rapidly at a high temperature than a low one, it is well 
now to increase the heat to a yellowish red, and even in 
certain cases to nearly a white heat. If the stirring of the 
assay has been constant during the various gradations of heat, 
the roasting at this point will be accomplished ; and the 
remaining operations of the assay may be proceeded with. 




42 


ROASTING ORES. 


This is the general plan of operation: but different sub¬ 
stances require for roasting a different degree of heat; for 
instance, copper pyrites requires a higher temperature than 
grey copper ore, and the heat employed must in every case 
be adapted to the substance to be roasted. Some substances, 
for instance, arseniates, sulphate of lead &c., cannot be 
roasted by heat alone. These require the addition of a 
carbonaceous body to remove the combined oxygen and 
allow the arsenic, sulphur, &c. to be completely roasted off. 
Carbonate of ammonia, in some cases, is also added to the 
mixture to separate the sulphates formed during the roasting 
of sulphides. 

In cases where the metallic bases of the sulphides are 
volatile, either as such, or as oxides, as, for instance, galena, 
sulphide of antimony, &c., a loss of metal will always result 
during the roasting process. 

It may be as well to mention here, that platinum capsules 
are useful in certain roasting operations. The sulphide of 
copper, iron, and molybdenum, are conveniently oxidised in 
this kind of vessel, without much fear of injury, provided 
fusion of the roasting substance be carefully avoided. Pla¬ 
tinum vessels must also be used in ascertaining the amount 
of ash in coal where the experiments are required to afford 
exact results. 

Reduction. —The process of reduction consists in removing 
oxygen or analogous element from any body containing it, 
usually by means of either carbonaceous matter or hydro¬ 
gen, or a body containing both of these elements, and leaving 
the metal behind, usually in the form of a melted button. 
The rationale of the operation is as follows, when oxide of 
lead is reduced with carbon :— 

2(PbO) +0 = 2Pb + C0 2 . 

In this first case we start with oxide of lead and carbon, 
and as a result we obtain metallic lead and carbonic acid. 

flie reaction between oxide of nickel and hydrogen is 
thus expressed:— 

NiO + II = 


Ni + IIO. 


REDUCTION. 


43 


Here we have at the commencement oxide of nickel and 
hydrogen ; and after the conclusion of the operation there 
remains metallic nickel and water which has volatilised. If 
the reducing substance contain both carbon and hydrogen 
the action will be thus, when a metal (e.g. lead) is reduced 
from its oxide, carbonic acid and water being formed :— 

3(PbO) + CH = 3Pb + C0 2 + HO. 

In the operation of reduction by the aid of carbonaceous 
matters, two methods are employed : in the one, charcoal, 
coal, sugar, starch, or any carbonaceous or hydro-carbona¬ 
ceous body, as argol, is mixed with the substance to be 
reduced ; in the other, the process of cementation is em¬ 
ployed. Where sulphides are to be reduced metallic lead 
or iron is usually employed to remove the sulphur. Gene¬ 
rally, however, the sulphides are previously converted into 
oxides by the operation of roasting, and the reduction is then 
effected by means of carbonaceous matter. 

The process of cementation is conducted by placing the 
oxide to be reduced in a crucible lined with charcoal, and 
covering it closely while it is in the furnace; the reduction 
proceeds gradually from the outside of the oxide to the 
centre of the mass. The time requisite for this operation 
depends on three circumstances—viz. the nature of the oxide, 
the degree of temperature, and the mass acted on. 

Some oxides treated this way are reduced very readily ; 
others, again, take a considerable time ; while certain of them 
do not appear to be acted on beyond the outermost layer. 
Of the first class is oxide of nickel; of the second oxide of 
manganese ; and of the third and last, oxide of chromium. 

Each of these classes of reduction has its advantages. 
The former, or reduction by mixture with carbonaceous 
matter, takes place very quickly and completely, but the re¬ 
duced metal is often mixed with carbon ; in the latter process 
the residue is comparatively pure, but it is not generally 
preferred, on account of the time and high temperature 
necessary. 

Reduction by hydrogen gas is very seldom employed ; it 
is, however, necessary in some cases, as for instance in the 


44 


FUSION". 


determination of the percentage of cobalt or nickel in a 
sample, where perfect accuracy is desirable. The operation 
is carried on in a tube of hard German glass, having a bulb 
blown in its centre, which is heated either by a spirit or 
gas lamp. Attached to it is a tube full of dried chloride of 
calcium, through which the hydrogen gas effecting the 
reduction passes to perfectly dry it. 

The bulb tube is weighed and the oxide introduced into 
it; it is again weighed, and the apparatus united by caout¬ 
chouc tubes ; hydrogen gas (see Reducing Agents) is then 
passed through it until the whole of the atmospheric ay* is 
expelled. Heat is afterwards applied till the bulb is bright 
red, and the current of gas continued until no more water 
from the decomposition of the oxide is formed ; the source of 
heat is then removed, and the current of gas continued until 
the apparatus is cold. The bulb tube, with the reduced 
metal, is then weighed, and the amount which it has lost re¬ 
presents the oxygen which the hydrogen lias removed. By 
subtracting this oxygen from the original weight of the 
substance, the difference gives the amount of metal in the 
amount of oxide operated on. 

Fusion. —This operation is sufficiently simple, and is em¬ 
ployed in all assays by the dry way, in order to obtain, in 
conjunction with the last process, a button or prill, as it is 
termed, of the metal whose assay is in progress. It is also 
a necessary step in the granulation of metals, the preparation 
of certain fluxes and alloys, also lead for the assay for silver, 
in order that a homogeneous ingot may be obtained. Some 
ores, such as those of copper, are melted instead of being 
roasted or calcined, in order to prepare them for reduction. 
Minerals are also melted per se 9 or with the addition of 
borax or carbonate of soda, in order to ascertain the best 
treatment to be adopted in a subsequent operation. Metals, 
too, are frequently melted to drive off other volatile metals. 
In this case the heat should be continued for some time, 
and should be very high, as it is difficult to remove the last 
traces of volatile metals. Ihus, in melting the spongy 
gold left behind in the retort after the distillation of gold 
amalgam, the ingot of gold almost always retains mercury, 


SOLUTION". 


45 


which can only be removed by repeated meltings at a very 
high temperature. In some cases the fusion is intended to 
be only partial, the object being to melt out an easily fusible 
part of the mineral, for instance, in assaying grey antimony 
ore, and different bismuth ores. 

Solution —In all cases where analysis in the wet way is 
required, the mineral must be either wholly or partially 
brought into the state of solution. The choice of a solvent 
necessarily depends upon the nature of the material under 
treatment. In some few cases water will be sufficient; but 
in the majority acids are required. Sometimes advantage 
will be derived by first extracting all that water will dis¬ 
solve, and then applying acids to the residue. In speaking 
of the minerals, &c., which require solution for their assay, 
the most appropriate solvents will be pointed out. In all 
cases heat promotes solution. 

Solution is best effected in glass flasks; clean Florence oil 
flasks are very appropriate for most purposes. They may 
be supported on a hot sand bath, or on a metal ring or coarse 
wire gauze, over the naked gas or spirit-flame. The flask 
slioidd be placed in a sloping position, so that when the 
liquid boils or effervesces from the escape of gas, the drops 
spirted up may strike against the sloping side, and run back 
into the liquid instead of being thrown out of the mouth. 

A porcelain dish may also be used, although from the 
great surface exposed these vessels are more appropriate for 
evaporation than solution. Beakers may likewise be em¬ 
ployed, but they should be covered over with an inverted 
funnel sufficiently large to rest within the top edge without 
slipping down more than about half an inch ; or a large 
watch-glass or dial-plate turned concave side upwards may 
be used as a cover. Both the funnel and dial-plate serve 
the double object of keeping out dust, and preventing loss 
of the liquid by projection of fine drops during ebullition. 

In many cases solution of the whole or part of a mineral 
must be preceded by its fusion at a high temperature with 
carbonate of soda, nitre, or some other flux. The fused 
mass must then be well extracted by boiling water, when 
tlie residue will usually be found soluble in hydrochloric or 


46 


DISTILLATION. 


other acid. Special instructions in this method of effecting 
solutions will be given in those cases where it is necessary. 

Distillation.— There are two distinct classes of this ope¬ 
ration : in the one, liquids are submitted to experiment, 
with the object generally of purifying them from substances 
which are non-volatile, and will consequently be left behind 
when the liquid comes over. Belonging to this class may 
be mentioned the distillation of nitric acid, the preparation 
of distilled water, and the separation of mercury from gold 
and silver amalgam. In the other kind of distillation, which 
goes by the name of dry distillation , solid bodies, as wood, 
coal, &c., are subjected to heat in order generally to ascer¬ 
tain the amount of gas or other volatile matter given off in 
the course of an experiment, from a certain quantity of the 


coal or other substance operated upon. 

In liquid distillations (as in the purification of nitric 
acid, &o.), retorts are used. The best form for general 
use is that which is furnished with a stopper at the upper 
part of the body, a (fig. 15), through which the liquid is 
f ig . i 5 . introduced ; the neck of the 

retort is then placed in that of 
a receiver, 5, over which a 
piece of wet cotton or woollen 
cloth is placed, and which must 
be kept cold by means of a 
stream of water from a funnel, 
c, the shaft of which is partially 
plugged up with cotton wool. 
Heat is then applied to the re¬ 
tort, and as much of the liquid 
as is desired, is distilled over 



into the receiver. It is advisable not to fill the retort more 
than two-thirds full, and to apply the heat at first very 
gently, otherwise there is a risk of breaking the vessel. 

A more convenient form of apparatus for distillation and 
condensation is shown at fig. 16, in which a Liebig’s con¬ 
denser is attached to the retort. Fig. 17 will show the 
construction of condensing apparatus. The cold water 
passes into the funnel above, is conveyed at once to the 





















DISTILLATION. 


47 


lowest, end ot the condenser, whilst the heated water passes 
off by the upper tube. 

Distilled water is a most important agent in the labora¬ 
tory; and, as much is needed, it is better to have a still 

Fig. 16. 



specially adapted for its production. Such a one is depicted 
at lig. 18, where A is the body of the still; B the furnace 
in which it is set (the still may also be placed in the porta¬ 
ble furnace, fig. 23, p. 62); C the still head ; D E the neck ; 


Fig. 17. 



F the worm ; IJ K L worm-tub containing cold water to 
condense steam generated in still; M N pipe to lead fresh 
cold water to bottom of worm-tub, while the warm water 
runs off at the top, as in Liebig’s condenser ; and P the 
vessel in which the distilled water is received. 

In the dry distillation of bodies, earthenware, glass, or 
iron retorts are employed ; but for small operations a tube 
of wrought-iron, about one inch internal diameter, and 













































48 


USE OF PNEUMATIC THOUGH. 


plugged at one end, is found to be a convenient form ot 

i DO # 7 . , . 

apparatus. It is placed with the substance contained in it 
in a furnace, and a small tube, either of glass or pewter, 
is lixed by means of a perforated cork to the open end of 
the large tube. The gas given off during the operation may 
be collected by the aid of the pneumatic trough. 


Fio. 18. 



It will be as well here to describe the pneumatic trough 
and jars, together with the requisite calculations for tem¬ 
perature, pressure, and moisture to be made in experiment¬ 
ing with gaseous bodies. The pneumatic trough is a vessel 
of square form, made of tin-plate or zinc, furnished with 
a shelf at the distance of about three inches from its upper 
part. This shelf, according to its size, is perforated with 
one, two, or more holes, each of which is furnished with a 
small funnel-shaped opening on the inferior side. This 
opening is for the purpose of receiving the mouth of a 
gas-delivery tube. The lower part of the trough ought 
to be furnished with a tap, for the purpose of drawing off 
the water when it is soiled. The gas jars are made of glass 
(the most convenient form is cylindrical), and graduated to 
cubic inches and tenths. Each of the jars may hold from 
50 to 100 cubic inches, or more, according to the quantity 
of gas expected to be furnished during each experiment. 





































EXAMINATION OF GASES. 


49 


To use the trough, proceed as follows : —Fill it with water 
to about two inches above the shelf, then fill one of the jars 
with water; place a ground-glass valve over its orifice, and 
then set it in an inverted position on the shelf over one of the 
holes with the funnel-shaped opening, into which introduce 
the gas-delivering tube. When the mouth of the gas jar is 
under water, the glass plate is removed. As soon as the 
gas passes off, by the aid of heat, from the coal or other 
body in the iron tube, or retort, whichever may have been 
employed, it will pass into the jar and displace the water. 
As soon as the jar is full it must be replaced by another, 
and so on until no more gas passes over The quantity 
produced in the experiment is then ascertained by reading 
off the graduations on the jars. It is, however, not the true 
quantity, as it is in a state of expansion by heat; or it has 
combined with a quantity of aqueous vapour from the water 
with which it was in contact; or, lastly, the barometer may 
not be at the height of 30 inches, from some change in the 
state of the atmosphere. If it were less than 30 inches 
it would cause the gas to appear greater in quantity ; if 
more than 30 inches it would appear less in quantity than 
it really was. The following is the method of making the 
calculations necessary for reducing the gas to its true 
volume:— 

Correction for Temperature.— It has been ascertained by 
the recent researches of Magnus and Eegnault that 100 parts 
of air or any other gas at 32° of Fahrenheit, when heated to 
212°, expand to 136*65 parts, the increase being 3 r 6 ^ 5 ths, 
or *3665 of the original bulk. If this be divided by 180, 
the number of degrees between 32° and 212°, it will be 
found that air expands —\, or in round numbers, ¥ | T th 
of its volume for each degree of Fahrenheit; and we can 
from this datum determine the expansion or contraction 
any gas would undergo for any given number of degrees of 
temperature. 

But supposing it be required to know what volume 100 
cubic inches of gas at 80° would occupy at 60°, the 
standard temperature, it must be kept in view that it is not 
T Jyth part per degree of the volume at 80" but of the 

E 



50 


EXAMINATION OF GASES. 


volume at 32°, which is to be deducted ; 401 parts of air at 
32° become 402 at 33°, and 403 at 34°, and so on ; so that 
at 60° they have increased to 510 parts, and at 80° to 530 ; 
so that we have a proportion between the bulks at 00° and 
at 80°, from which the question may be determined, for :— 

Volume at 80° Volume at 60° Cubic inches Cubic inches 

401 + 48 : 401 + 28 :: 100 : 06 288 


or the reverse, supposing it were wished to ascertain the 
real volume at 60° of 100 cubic inches of gas at 40°. 

Volume at 40° Volume at 60° Cubic inches Cubic inches 

401 -h 8 : 401 + 28 :: 100 : 104*008 


Correction for Pressure.— As before stated, the standard 
pressure is 30 inches of mercury, and the law must be kept 
in mind that the bulk of a body or gas is inversely propor¬ 
tionate to the weight, and directly proportionate to the 
pressure ; so that if we had 100 cubic inches of air when 
the barometer was 29 inches it would be as :— 


30 : 29 :: 100 : 96*6 

or if the barometer stood at 31 inches when the 100 cubic 
inches were measured, it would be as :— 

30 : 31 :: 100 : 103*33 

' so that the rule is :—as the mean pressure is to the 
observed pressure, so is the observed volume to the true 
volume. The correction for temperature or pressure may 
be made indiscriminately, the result being the same in either 
case. 

Correction for Moisture. —This correction must be made 
after the two previous. As before mentioned, the elastic 
force of the aqueous vapour Causes the gas with which it 
may be mixed to expand, and by reference to tables founded 
on calculations upon the force of steam at different tempera¬ 
tures, the amount of correction may be easily ascertained. 
Thus, for 100 cubic inches of a gas saturated with vapour 
properly corrected to the temperature of 60° and 30 inches 
pressure, we wish to know the equivalent bulk of the dry 
gas. The observed volume is partly due to the expansion 
occasioned by the vapour ; and this proportion will be, in 





SUBLIMATION. 


51 


proportion to the whole, as the elasticity of the vapour is to 
the total elasticity ; therefore :— 

Elasticity of air Elasticity of vapour Cubic inches Cubic inchos 

30-000 : 0-560 :: 100 : 1-86. 

The volume of the dry gas is therefore :— 

100 — 1*86 = 98-14 cubic inches. 

Sublimation. —This operation is a kind of distillation in 
which the product is obtained under the solid form. The 
apparatus which may be employed for this purpose are 
tubes, flasks, capsules, or crucibles. Florence flasks are 
exceedingly useful: they may be sunk in a sand bath, and 
the sublimed substance received directly into another flask, 
or by passing through an intermediate tube. Sometimes, 
however, it is difficult to entirely remove the sublimed sub¬ 
stance ; and in order to avoid this inconvenience, Dr. Ure 
has proposed the following very excellent subliming appara¬ 
tus :—It consists of two metallic or other vessels, one of 
which is flatter and larger than the other. The substance 
to be sublimed is placed in the smaller vessel, and its open¬ 
ing is covered by the larger filled with cold water, which 
may be replaced from time to time as it becomes hot. The 
sublimed substance is formed on the lower part of the upper 
vessel. A large platinum crucible, filled with cold water, 
and placed on the top of a smaller one, answers the purpose 
of the before-mentioned apparatus very well. 

Scorification : Cupellation.— These operations will be 
described under the head of Silver Assay. 




CHAPTEE IV. 


PRODUCTION AND APPLICATION OF HEAT. 

Furnaces for assay purposes may be heated either by solid 
fuel, oil, or gas, and they may be divided into wind and 
blast furnaces. In the former the fire is urged by the or¬ 
dinary draught of a chimney; and in the latter by means 
of bellows or artificial blast. We shall commence with 
the former, as they are in most common use. They are 
of various kinds, according to the purposes for which they 
are required. The three principal kinds are those for 
fusion, calcination, and cupellation. Coal, coke, and char¬ 
coal, are the fuels employed, and the merits of each will be 
particularly discussed. Blast furnaces are only employed 
for the purpose of fusion, although their forms are various : 
charcoal and coke are the fuels most in use, but oil and gas 
blast furnaces are used in small laboratory operations, and 
for many purposes they are preferable to other furnaces, on 
account of their freedom from dust and dirt, and the perfect 
control the operator possesses over the heat. 

Furnaces consist of certain essential parts—viz. first, the 
ash-pit, or part destined to contain the refuse of the com¬ 
bustible employed; secondly, the bars on which the fuel 
rests; these are sometimes made movable, or fixed to a 
frame; the former arrangement is more convenient, as it 
allows clinkers and other refuse matters to be readily re¬ 
moved ; thirdly, the body of the furnace in which the heat 
is produced ; and lastly, in wind furnaces, the chimney by 
which the heated air and gaseous products of combustion are 
carried off. 

Calcining Furnace.— Calcining furnaces are small and 
shallow, because a high temperature is not required. They 


CALCINING FURNACE. 


53 


may be made square or circular; the former are most 
readily constructed, and where many crucibles are to be 
heated at once, they are preferable to the circular; but the 
latter give the greatest degree of heat with the least possible 
consumption ot fuel, and are to be preferred on that ac¬ 
count where one crucible only is to be ignited. 

The body of the furnace is best made with good bricks, 
lined with Welsh lump, fire-bricks, or a mixture of Stour¬ 
bridge clay and sand. It is also desirable that a plate of iron 
with a ledge be placed over the upper part of the furnace to 
protect the brickwork from blows with crucible tongs, &c., 
and to keep it in its place when disturbed by sudden altera¬ 
tions of temperature. The bars of the furnace may be 
either in one single piece, or made up of several bars of iron 
fastened to a frame. They ought to be as far as practical 
from each other, and must not be too large, although large 
enough not to bend under the weight of the fuel and cruci¬ 
bles, when they become hot, and they must not be so far 
removed from each other as to allow the coke or charcoal 
to fall through easily. Lastly, the more readily the air can 
find access to the centre of the fuel, the higher will be the 
temperature produced in the furnace : very simple assays 
occasionally fail, only because the bars are either too large 
or too close together. 

The Ash-pit is an open space under the bars, which 
serves as a receptacle for ashes, clinkers, &c., produced 
during the time the furnace is in use. It should have the 
same area as the furnace, and be completely open in front, 
so that the air may have free access : it is well, however, for 
the sake of economy, to furnish this opening with a hinged 
door, having a register plate fixed in it, so that the draught 
may be reduced, or entirely shut off, in order that the fire 
may be extinguished when desirable, and fuel saved which 
otherwise would be burnt in waste. 

Chimney. —Calcining furnaces generally have no fixed 
chimney, but are covered with a movable one when a 
greater degree of heat is required. This chimney may be 
about five feet high, the diameter of the furnace at the 
bottom, and tapering oil* to about two-thirds of that diameter 


54 


WIND FURNACE. 

fit the top. It is made of strong plate iron, furnished with 
a wooden handle. The lower part is provided with a door, 
by means of which the interior of the furnace may be 
examined without disturbing the whole arrangement of the 
chimney, and consequent cooling of the contents of the 
furnace. 

If, during the course of any experiment, noxious or 
offensive vapours are expected to be given off, the furnace 
must be so arranged that they may be introduced into 
a flue, by fastening a piece of iron plate pipe, furnished 
with an elbow-joint, on to the movable chimney before 
spoken of. 

Evaporating Furnaces. —The furnaces just described 
answer exceedingly well in the absence of gas, for heating 
small flasks, evaporating basins, &c., when surmounted by a 
tripod stand or sand bath. This is necessary, as many assays 
by the dry way are preceded or followed by certain opera¬ 
tions in the wet way. 

The Hood. —In order to prevent certain gases or vapours 
from fires, evaporating basins, &c., from entering into the 
laboratory, a large metal covering, termed a hood, is em¬ 
ployed, terminating in a chimney having a good draught. It 
is best made of plate or galvanised iron. 

Fusion Furnace: Wind Furnace.— The wind furnace, pro¬ 
perly so called, is a furnace provided with a chimney, and 
capable of producing a very high temperature. 

Wind furnaces are generally square, but if more than four 
crucibles are to be heated at one time, they may be made 
rectangular, the chimney being placed at one of the long 
sides. When the furnace is required to hold but one pot, 
it may however be made circular. 

The body of the furnace ought to be made of good bricks, 
solidly cemented with clay, and bound by strong iron bands. 
The bricks must be very refractory, and capable of sustaining 
changes of temperature without cracking. They are ordi¬ 
narily made with the clay used in the manufacture of 
crucibles. In some cases bricks are not used for the lining 
of this kind of furnace ; for instance, a mould of wood is 
placed in the centre and the open space between the surface 


WIND FURNACE. 


55 


of that and the outer brickwork is filled with a paste of very 
refractory clay, each layer being well beaten down. When 
the space is filled, the case is withdrawn, and the crust of 
clay dried with much precaution, every crack that may be 
caused by unequal dessication being filled up as fast as 
formed. This method of manufacture is very applicable to 
circular furnaces. In every case, however, it is necessary to 
border the edge with a band of iron to prevent injuries from 
tongs or pots. By using a mixture of 1 part of refractory 
clay, and 3 to 4 parts of sifted quartz sand, no cracks are 
formed during desiccation. This mixture is used on the 
Continent for the interior fittings of Sefstrbm’s blast furnace, 
as well as for larger blast furnaces for manufacturing pur¬ 
poses. It is said to stand a high temperature exceedingly 
well. 

Makins* recommends for small furnaces the second kind 
of bricks, known as Windsor, or in the trade P. P. bricks. 

‘ These are of a red colour, very siliceous, but soft, easily cut 
and shaped, and yet standing heat very well. The best 
method of cutting them is by a piece of zinc roughly notched 
out as a saw, and then the more accurate figure required 
may readily be given them by grinding upon a rough flat 
stone. In this way the small circular furnace formerly made 
by Newman, and sold by him as his ‘ universal furnace,’ is 
lined by cutting the bricks with care to the radii of the circle 
they are to form, when they key in, like an arch, and so 
need no lining whatever.’ 

The Ash-pit.— On the one hand, it is well to have the 
power of cutting off access of air into the body of the furnace 
by the lower part, either to put out the fire entirely, or to 
deaden it whilst putting in a pot; and, on the other, to attain 
the maximum of temperature, we must have the means of 
allowing the air to pass with the greatest possible facility into 
the furnace. In order to do this it is necessary to furnish 
the ash-pit with doors, or valves, whereby the quantity ad¬ 
mitted may be regulated as desired. It is advantageous to 
lead the air to the ash-pit from a deep and cold place, by 


* Making's Metallurgy, p. 8fc. 


56 


WIND FURNACE. 


means of a wide pipe. A chimney of less height will then 
be required. 

The Bars are made in one piece, or are made up of 
moveable pieces of metal; the latter arrangement is the most 
convenient. Wherever a wind furnace is in use, the superior 
opening is closed by a cover made of a fire-tile, encircled 
with iron. 

The Chimney is a very essential part of a wind furnace : 
it is on its height and size that the draught depends, and, 
in consequence, the degree of heat produced within the 
furnace. In general, the higher and larger the chimney 
the stronger is the draught; so that, by giving it a great 
elevation, exceedingly high temperatures may be obtained. 


Fig. 19. 



But there is a limit which it is useless to pass in a furnace 
destined for operations by the dry way; and besides this, 
the building a very high chimney presents many difficulties, 
and much expense, so that in laboratory operations, where a 
very strong current of air is required, recourse is had to a 
pair of double bellows. A temperature can be produced in 






















































BLAST FURNACE. 


57 


a wind furnace sufficiently strong to soften the most re¬ 
fractory crucibles by means of a chimney from thirty-six to 
forty feet high. 

Chimneys are generally made square or rectangular, and 
have interiorly the same dimensions as the body of the 
furnace. About two feet above the upper part of the 
furnace they are furnished with a register or damper, by 
means of which the current of air may be regulated, or 
entirely stopped at will. The damper is a plate of iron 
sliding into a small opening across the chimney. 

A wind furnace of the kind above described is represented 
by fig. 19. 

The left hand figure in 19 is the plan, the middle an 
elevation, and the right is a sectional view. A the body of 
the furnace in which the crucibles to be heated are placed, 
G the bars, and P the ash-pit; the cover is formed of a thick 
fire-tile of the requisite size firmly encircled by a stout iron 
band, and furnished with a handle for convenience in 
moving it; B the flue, C the chimney, R the damper ; II a 
hood over the furnace, supported by iron bands h h h ; M 
the handle of a ventilator P, which serves to carry off hot 
air and fumes from furnace when open; and, finally, S, a 
small sand bath, in which to set the red hot crucibles when 
taken from the fire : one foot square inside the fire-place of 
the furnace is a very good and convenient size ; the remainder 
will then be in proportion. 

Blast Furnaces,— In this species of furnace, the air 
necessary to keep up the combustion is forced through the 
fuel by means of a blowing apparatus, instead of being 
introduced by the draught of a chimney as in the wind 


furnace. 

The most convenient apparatus for forcing air into a 
furnace is a double bellows; a fan may be used, but it is not 
so powerful. 

The quantity of air passing into a furnace varies with the 
length of the assay, and ought to increase gradually as the 
temperature becomes higher. 

The following is the description of a most excellent blast 
furnace which has been in use for some years in the labora- 



58 


BLAST FURNACE. 

tory of the Royal Institution :—The temperature produced 
by it is extraordinary, considering the small amount of time 
and fuel employed. It is sufficiently powerful to melt pure 
iron in a crucible in ten to fifteen minutes, the lire having been 
previously lighted. It will effect the fusion of rhodium, and 
even pieces of pure platinum have sunk together into one 
button in a crucible subjected to its heat.* All kinds of 
crucibles, including the Cornish and Hessian, soften, fuse, and 
become frothy in it; and it is the want of vessels which has 
hitherto put a limit to its application. The exterior (fig. 
20) consists of a black-lead pot, eighteen inches in height, 
and thirteen inches in external diameter at the top ; a small 
blue pot of seven and a half inches external diameter at the 
top had the lower part cut off, so to as leave an aperture 
of five inches. This, when put into the larger part, rested 
upon its lower external edge, the tops of the two being 
level. The interval between them, which gradually in¬ 
creased from the lower to the upper part, was filled with 
Fig. 20. pulverised glass-blowers’ pots, to which 
enough water had been added to moisten 
the powder, which was pressed down by 
sticks, so as to make the whole a com¬ 
pact mass. A round grate was then drop¬ 
ped into the furnace, of such a size that it 
rested about an inch above the lower 
edge of the inner pot: the space beneath 
it, therefore, constituted the air-chamber, 
and the part above, the body of the fur¬ 
nace. The former was inches from the grate to the 
bottom, and the latter 7^ inches from the grate to the top. 
Finally, a longitudinal hole, conical in form, and 1^ inches 
in diameter in the exterior, was cut through the outer pot, 
forming an opening in the air-chamber at the lower part, 
its use being to receive the nozzle of the bellows by which 
the draught was thrown in. 

Sefstrom’s Blast Furnace, obtainable at most chemical 
instrument makers, is also very powerful and convenient; 

* Faraday. 













MUFFLE FURNACE. 


59 


it consists of a double furnace. It is made of stout sheet 
iron, lined with fire-clay, and is used with coke, or charcoal 
and coke, cut into pieces of about a cubic inch in size. 
The blast of air is supplied by a powerful blowing-machine 
It will readily produce a white heat. Indeed the limit to 
its power seems to be the difficulty of finding crucibles or 
interior furnace fittings which will stand the temperatures 
produced in it without softening. Kersten states that he 
increases the heat in Sefstrom’s blast furnace by using a hot 
blast. 

H. Ste-Claire Deville has employed for melting platinum 
a furnace of 30 centim. height, and 28 centim. wide, which 
rests upon a cast-iron plate full of holes. This is connected 
with a forge bellows. After blowing for a few minutes, the 
temperature of the furnace will have reached the highest 
possible degree, but this zone of maximum heat only extends 
to a small height above the bottom of the furnace. Above 
this point a considerable quantity of carbonic oxide gas is 
formed, which burns with a very long flame. The heat 
produced in this furnace is so high, that the best crucibles 
melt, and only crucibles made of good and well burned 
lime can be used. 

The Muffle, or Cupel Furnace, is a furnace in the centre 
of which is placed a small semi-cylindrical oven, which is 
termed the muffle. These furnaces were in use as early as 
the thirteenth century. Their construction and dimensions 
depend:— 

I. On the temperature which the furnace is intended to 
produce; 

2. On the number of cupellations required to be per¬ 
formed at one time ; and 

3. On the kind of fuel used. 

The muffles are mostly made of refractory clay, generally 
in one piece, but it is best to make them in two pieces; the 
bottom being one, and the cover or vault the other. 

Muffles are sometimes made of cast iron—cast in one 
piece. They are useful in small furnaces intended for 
cupellations only. 


GO 


MUFFLE FURNACE. 


Muffle furnaces must always be provided with a good 
chimney to carry off the hot gases. 

The muffle, being completely surrounded by ignited fuel, 
acquires a very high temperature, and in its interior all 
operations requiring the presence of air, and which can¬ 
not be carried on in contact with carbonaceous matters, 
may be performed—such as roastings, scorifications, and 
cupellations. 

When from ten to twenty cupellations have to be effected 
at one time, large brick furnaces are employed; and, in 
consequence, much fuel is consumed to waste in these when 
only a few cupellations are required. This has occasioned 
many persons to endeavour to form small furnaces, where 
one or two cupellations may be carried on with the smallest 
possible quantity of fuel. 

MM. Aufrye and d’Arcet have contrived a furnace which 
is capable of fulfilling all these conditions. 

The furnace is elliptical, and about 7 inches wide and 18 
high ; its ash-pit lias but one circular opening, and its 
height is such, that when the furnace is placed upon it, and 
the whole upon a table, the assayer can, when seated, readily 
observe the course of the assay within the muffle. The 
hearth has five openings, in one of which the muffle is placed; 
in another, a brick to support it; a third is for the purpose 
of introducing a poker to stir the ashes, and make them fall 
through the grate-lioles : this can be closed with a small 
earthen plug; and lastly there are two round holes, placed 
in its largest diameter, to facilitate the introduction of air, 
either by draught or a pair of bellows, as the case may 
require. The support for the fuel is generally a plate 
of earthenware, pierced with holes, and bound round 
with iron wire to keep it together in case it cracks by 
changes of temperature ; but it is better to use an iron 
grating. 

The dome of the furnace has a circular opening, which 
can be closed by a plug of earthenware : this opening serves 
for the introduction of the fuel. A chimney is necessary to 
increase the draught; it is made of sheet iron, and may be 
from to 2 feet in height, and ought to fit the upper part 


MUFFLE FURNACE. 


61 


of the dome very exactly. At its base there is a small 
gallery, also of sheet iron, in which it is intended to place the 
new cupels, so that they may be strongly heated before intro¬ 
duction to the muffle. This saves many of them from fracture. 

M.M. Aufrye and d’Arcet have estimated the quantity of 
charcoal necessary to heat this furnace. The following are 
comparative experiments:— 



Silver 

Lead 

Time 

Standard 

Charcoal 

No. 

employed, 

employed, 

of assay, 


used, 

grains 

grains 

minutes 

thousandths 

grains 

1 

1 

4 

12 

947 

173 

2 

1 

4 

11 

950 

86 

3 

1 

4 

13 

949 

93 

4 

1 

4 

10 

949 

60 


Coke or charcoal may be used in this furnace, but the fire 
must be lighted by means of charcoal alone, as coke is very 
difficult to inflame in a cold furnace. When it is red-hot, it 
may be fed with coke, or, better still, a mixture of coke 
and charcoal. 

Where great numbers of cupellations have to be made at 
once, the following form of brick furnace is requisite. 

Fig. 21 shows an elevation of the furnace ; fig. 22 shows 
a section. The interior of the furnace is of fire-brick ; the 
exterior of common brick. The upper part is protected by 
a plate of iron, and the superior opening, through which the 
fuel is introduced, is covered when necessary by a large fire- 
tile strongly encircled with an iron band, to which are 
attached two handles, by which the whole can be moved. 

The muffle opening as seen partially open in the diagram, 
can be entirely closed by means of two sliding doors, made 
of sheet-iron, running in a stout wrought-iron frame, built 
into the brickwork. Immediately below the muffle entrance 
are two movable bricks; these close the openings through 
which the fire bars are introduced; and still lower down is 
the ash-pit door, furnished with a register for the better 
regulation of the current of air required by the furnace. In 
fig. 22 is shown a brick built into the back of the furnace, 
on which the close end of the muffle is supported. This 
• brick may, however, be replaced by a crucible or fire brick 
standing on the bars of the furnace. 


62 UNIVERSAL FURNACE. 

A very useful furnace for small operations is one which 
has been aptly termed the 4 universal furnace,’ as it is capable 

Fig. 21. Fig. 22. 



of performing all that is required of any furnace in an assay 
(see figs. 23 and 24, elevation and section). It is to be much 


Fig. 23. 


Fig. 24. 



recommended for its durability, cheapness, and its small size 
compared with the heat it can produce. It is constructed 






















FURNACE OPERATIONS. 




externally of sheet iron, very stout, and is lined with fire¬ 
brick, not cemented together, but ground and keyed as an 
arch, so that it can never fallout till it is completely useless. 
Its height is about feet and diameter 1 foot; internal 
diameter 8 inches and depth of fire-place feet. It. is 
furnished with five doors, one in the ash-pit and four in the 
body of the furnace, two in the front, one above the other, 
and two opposite each other, at the sides. The cover serves 
as a sand-bath, and when that is taken off there is a series of 
cast-iron rings, fitting the top of the furnace, for the purpose 
of placing basins either for the purpose of evaporation, 
calcination, or roasting. The two opposite holes serve for 
the introduction of a tube in operations where it is requisite 
to pass a gas over any body at a red heat. In the lower 
hole in front, can be placed a muffle for roastings and 
cupellations, introducing fuel and crucibles by the upper 
one; it also serves as an opening through which the state 
of the furnace can be seen, or the progress of any assay 
observed. 

Iron, manganese, nickel, and cobalt, can be fused in this 
furnace, when it has a flue of about thirty feet in height 
attached to it, and by closing the ash-pit door, the dullest 
red heat, for gentle roastings, can be obtained. 

FURNACE OPERATIONS. 

Crucibles must be carefully supported in the fire, and 
must always be covered. They must stand solidly, and be at 
equal distances from the sides and bottom of the furnace, so 
as to receive a like share of heat, and they must be completely 
surrounded with the fuel. If a crucible is supported on 
the grate bars of a furnace the draught of cold air will prevent 
the bottom from getting hot. If it is supported on the fuel, 
the bottom gets heated quickly, but the fuel in burning away 
allows the crucible to fall down, and may cause the loss of 
the contents. For these reasons a crucible should always 
be supported on a piece of fire-brick about three or four 
inches high. In many cases an old crucible inverted will 
serve as "a convenient support. The fire must be got up 


G4 


FURNACE APPARATUS. 


gradually, so as to prevent the sides of the furnace and the 
crucibles within from cracking from the sudden increase of 
heat. No time is saved by urging the fire strongly at first, for 
crucibles are bad conductors of heat, and a high temperature 
at v the commencement scarcely causes the heat to penetrate 
to the interior faster than a moderate redness. After the 
furnace has arrived at a full red heat, more air may be given, 
and in from about twenty minutes to one hour, the assay will 
be finished. During the time the furnace is in full action, the 
cover must be occasionally removed to add more fuel, if any 
open spaces occur round the crucibles ; also to press the fuel 
close to the pots. When the pots are taken out they may 
be placed on the anvil or in a sand-bath, and allowed to cool 
gradually, before they are broken to examine their contents. 

In commencing a second assay immediately in the same 
furnace, certain precautions must be taken to insure success. 
In the first place, all ash and clinker must be removed from 
the grate, by means of a crooked poker ; secondly, the fuel 
must be pressed down firmly; and lastly, a layer of fresh 
combustible must be placed on the fire, and before that is 
ignited the crucibles must be arranged upon the support and 
the spaces about them be filled with coke or charcoal, as the 
case may be, and the assay be proceeded with as before. 

In executing many assays, one after the other, a great 
saving of fuel is effected, for the furnace is not allowed time 
to cool. 

Auxiliary Apparatus.— Ordinary assay furnaces require 
very few instruments; they are, firstly, pokers or stirring 
rods, made of stout bar-iron : these may be straight, as for 
stirring the fuel from the top of the furnace, so as to fill up 
cavities formed by uneven combustion ; or curved, for clear¬ 
ing the bars from below from clinkers and ashes. Straight 
and curved tongs are also required; for small crucibles the 
blacksmith’s common forge tongs are the most suitable ; tongs 
with semicircular ends (see fig. 25) are very serviceable for 
larger crucibles. The tongs a, are particularly adapted for 
removing large cupels or calcining tests from the muffle ; the 
tongs b and c are used for lifting heavy crucibles from the 
wind or blast furnace. In case the eyes of the operator 


FURNACE TONGS. 


65 


are weak, it is advisable to make use of a pair of deep 
neutral-tint spectacles. Most of the radiant heat from the 
interior of a furnace may be cut off by holding before the 
face a large sheet of window glass; or the operator may look 
at the reflected image in a looking-glass instead of looking 


Fig. 25. 




direct into the furnace itself. Some assayers recommend 
the use of masks for the face and gloves for the hands; but 
these are not needed. In cupel furnaces, both curved and 
straight pokers or stirring rods are required; also a curved 
rod made of lighter iron, to be used in closing the sliding doors, 
slightly moving cupels, &c. The tongs used vary in form 
(see fig. 26). a represents very light elastic tongs or pincers 
employed in the introduction of lead and other matters 


a 


b 


c 

to the cupel: b shows the tongs for holding the scorifier; the 
curved part fits the lower part of the scorifier, and the upper 
or single part passes over the upper part of the scorifier, 
so that its contents may be emptied into the proper mould 
without fear of its slipping from the operator’s grasp : c 
represents the tongs used in moving cupels; they are slightly 
curved, so that the cupels from the back part of the muffle 


Fig. 26. 

























G6 


INGOT MOULDS. 


may be removed without disturbing those in front. Fig. 
27 shows the plan and section of the ingot mould, into 


Fio. 27. 



ooo 

ooo 

ooo 


which the contents of the scorifiers are poured : it is made 
of thin sheet iron, and the depressions for the reception 
of the fused lead, slag, and ore are hammered out. Fig. 


Fig. 28. 



28 is a wrought-iron ladle, in which lead clippings, &c., 
are melted, in order to obtain a fair average of a 

large quantity; and fig. 29 re¬ 
presents the ingot mould into 
which the fused lead, or other 
metal, is poured. Other special 
apparatus will be described under 
the assay in which they are re¬ 
quired. 

Furnaces are heated with anthracite, coke, and charcoal, 
and sometimes with a mixture of the two latter ; coal is 


Fig. 29. 







FUEL FOR FURNACE. 


67 


very seldom employed, and therefore will not be much 
spoken of; coke is the principal combustible used in assaying. 
Calcining furnaces ought to be heated with charcoal alone, 
because coke employed in small quantities ignites and burns 
with too much difficulty. All fuel contains certain fixed 
matters which remain after combustion, and which constitute 
the ash. This ash fuses or agglutinates together, and when 
a certain quantity is formed, if it be not removed, the fire 
will decrease in intensity, and finally die out. As all com¬ 
bustibles do not contain the same amount of ash, they should 
be carefully selected ; those containing the least are to 
be preferred; in the first place, because, weight for weight, 
they contain more available fuel; and secondly, because 
they can be used in a furnace a longer time without the 
formation of so much clinker. The composition of the ash 
likewise merits much attention. 

Charcoal contains, in general, from 3 to 4 per cent, of ash, 
the chief components of which are carbonates, lime and 
potash. Certain other matters are also present, as phospho¬ 
ric acid, oxide of iron, manganese, &c., but these are in very 
minute proportions. The ash is not fusible per se, and if it 
does not meet with any substance capable of combining with 
it, it passes through the bars as a white powder; but when 
the potash predominates, it exercises a corrosive action 
on the bricks with which the furnace is lined, as also on 
crucibles, lutes, &c., by the formation of a fusible silicate of 
potash, which in course of time runs down the sides of the 
furnace, and chokes the bars. Whenever the ash is in very 
small proportion to the charcoal, its fusion is rather useful 
than otherwise, because it forms a species of varnish, which, 
penetrating the surface of the bricks and lutes, gives them 
solidity by binding them together with a cement, forming 
part of their substance. 

The proportion of ash which coke contains is very vari¬ 
able ; some commercial samples contain from 8 to 10 per 
cent., while others made from very pure coal, give but 2 to 3 
per cent. ; so that this fuel also ought to be carefully chosen. 
The nature of this ash is different from that of charcoal; it 
consists principally of oxide of iron and clay. The former 


68 CHARCOAL—COKE. 

is produced from the pyrites which coal generally contains. 
The clay is similar to the carbonaceous schists, not very 
fusible by itself, but nevertheless capable of softening. 
When pure, it forms a slag, which attacks neither the bricks 
nor crucibles. This happens very rarely ; it is more often 
that oxide of iron predominates, and this by contact with the 
carbonaceous matter, becomes reduced to the state of prot¬ 
oxide, and is then not only very fusible, but exercises 
on all argillaceous matters a very corrosive action, so that 
crucibles are very seriously injured, and the sides of the 
furnace require frequent repairs. 

Weight for weight, coke and charcoal give out nearly the 
same quantity of heat; but in equal bulks, the former de- 
velopes much more heat, because its density is greater: 
from this difference in the calorific power of coke and char¬ 
coal, it results that in the same furnace the former produces 
a greater degree of heat than the latter ; and at high tem¬ 
peratures the difference has been proved to be nearly 10 
per cent. In order to account for this, we must consider, 
firstly, that in a given space the quantity of heat produced 
in a certain time (and, in consequence, the temperature) 
depends on the amount of fuel burnt, and increases with its 
weight; secondly, that combustion takes place but at the 
surface of the masses, whatever may be the nature of the 
fuel; from which may be deduced, that the weight of fuel 
burnt in an unit of time ought to be exactly proportionate 
to its density; and, in consequence, the densest fuels, fur¬ 
nishing the most food for combustion, ought to give out the 
greatest heat. But, as for the same reason they consume 
a larger proportion of oxygen, they require, in order to 
produce the maximum effect, a more rapid and stronger 
current of air. 

It is clear from what has been stated concerning the 

o 

relative properties of coke and charcoal, than when the 
former can be procured of good quality, and especially 
when the ash contains but little oxide of iron, it ought to 
be preferred to charcoal, for assays requiring a high 
temperature. 

This being an important subject, it has been thought 


EFFECTS OF FURNACES. 


no 


advisable in this edition to devote a special chapter to the 
assay of fuel. (See chapter v. p. 13S.) 

A very essential condition in obtaining the maximum 
effect of a furnace, the importance of which can alone be 
appreciated by experience, is to choose pieces of fuel of 
a suitable size. If, on the one hand, a shovelful of coke or 
charcoal be taken at random, it generally contains the dust 
and dirt found in most fuel, and which, by filling the inter¬ 
stices, prevents the air from passing as required, and conse¬ 
quently renders the combustion slow. On the other hand, 
if a furnace be filled with large pieces, considerable spaces 
are left between them, so that but a comparatively small 
surface is exposed to the action of the atmospheric oxygen, 
and a correspondingly small quantity of fuel is consumed in 
a given time; so that the maximum heat can never be 
obtained. In order to produce the desired result, it is 
necessary that the pieces shall have a certain mean size, and 
experience has proved that pieces about 1 inch to 1^ inches 
diameter produce the best effect. These may be selected 
by sifting the coke through two strong wire sieves, one of 
which has meshes about 1J inches square, and the other 
about 1 inch square. The coke which passes through the 
larger one, but will not go through the smaller sieve, will be 
the right size for the furnace. 

The Effects produced by Wind and Blast Furnaces.— 
Assays by the dry way can be made either in wind or blast 
furnaces. In either of them, the degree of heat depends 
upon the volume of air which passes through the fuel in 
the same time ; but, cceteris paribus , large furnaces produce 
more heat than small ones, because comparatively less heat 
is lost by radiation in the former than the latter. 

In a wind furnace, the maximum of heat is limited by the 
size of the chimney, and in a blast furnace, by the dimensions 
of the bellows ; but by weighting the latter, more or less, 
the force of the blast can be increased, and, in consequence, 
the temperature to a considerable extent. In this respect 
blast have the advantage over wind furnaces. 

In the latter, the draught increases in proportion as the heat 
becomes more intense in the furnace, so that the tempera- 


70 


FOCUS OF MAXIMUM TEMPERATURE. 


ture producible increases progressively. In a blast furnace, 
the bellows can be weighted and worked as heavily as pos¬ 
sible at once, and by opening all the apertures for receiving 
air, the maximum temperature can be produced more 
rapidly than in a wind furnace; but this is of little use, 
because as heat passes very slowly through the substance of a 
crucible, when the object is to fuse its contents it must be 
heated gradually, so as to avoid running the risk of softening 
the crucible before its contents are acted upon, or even 
scarcely made warm. 

Wind furnaces are, however, much more serviceable and 
economical than blast, because they work themselves, and 
do not require the service of a man to attend to the bellows. 
A blast furnace is used in a laboratory, in certain cases; for 
instance, when a single crucible has to be submitted to an 
intense heat, and when the furnace is small, and the bellows 
large, in which case the operation resembles a blow-pipe assay. 

In whatever manner the air is introduced into any kind 
of furnace, either wind or blast, it is evident that the quan¬ 
tity of heat developed in equal-sized furnaces depends upon 
the quantity of air introduced in the same time : but the 
degree of temperature is not the same in different parts of 
the furnace, and the distribution of heat varies according to 
the manner in which the air is introduced into the midst of 
the fuel. The side over which the air passes, is kept cold 
by the current, on which account fire-bars last a long time 
without becoming oxidised, but the heat rapidly augments 
up to a certain distance from the bars, at which place it 
arrives at its maximum ; above that it diminishes rapidly, 
because the air is nearly deprived of its oxygen. Experi¬ 
ment has proved that this maximum is about to 3 inches 
above the bars or tuyeres. 

In common wind furnaces the air enters through the spaces 
between the horizontal bars which form the bottom of the 
furnace, and the crucibles are placed on a stand which rests on 
these bars. By this means the lower and centre part of the 
crucibles, in which parts the matter to be fused is placed, are 
exactly situated in the maximum of heat, but the stand 
being constantly kept cold, by the contact of a current of air, 


OIL AND GAS FURNACES. 


71 


establishes a continual draining or carrying away of heat 
from the interior of the crucible outwards, so that the sub¬ 
stance submitted to assay can only arrive at the maximum 
temperature after a length of time, and the maximum then is 
always inferior to that in the mass of fuel. It is on this ac¬ 
count that assays in a blast or wind furnace generally occupy 
from one hour to two hours. The author has found that the 
time may be reduced to half that just stated, if a good solid 
foundation of fuel be made, and the crucible placed on that, 
and well surrounded by coke, constantly kept close to the 
pot and the sides of the furnace : in this manner the cooling 
effect of the stand is removed, and the consequent maximum 
effect of the furnace produced, but then there is danger of 
the supporting fuel being burnt away from the crucible and 
the latter getting upset. 

OIL AND GAS BLAST FURNACES. 

It sometimes happens that metallurgists and assayers have 
occasion to melt metals at a white heat, but do not wish to 
heat a large furnace for the purpose. In these cases either 
the gas or oil furnaces, now to be described, will prove very 
useful. 

Oil Furnaces. —Mr. Charles Griffin, the son of the well- 
known chemical instrument maker of that name, described, 
in the 4 Chemical News,’ for January 2, 1864, an oil lamp, 
which is not only as powerful in action as the best gas 
furnaces, but almost rivals them in handiness and economy. 

Description of the Apparatus. —The oil-lamp furnace is 
represented in perspective by fig. 30, and in section by 
fig. 31. It consists of a wick-holder, an oil-reservoir, and a 
fire-clay furnace ; to these must be added a blowing-machine 
for the supply of atmospheric air. 

The oil-reservoir is represented at a, fig. 30 ; it is made of 
japanned tin-plate, mounted on iron legs, and fitted with a 
brass stop-cock and delivery-tube. Its capacity is a little 
more than a quart. The wick-liolder is represented at b , 
and the upper surface of it by the separate figure c, fig. 32. 
The wick-holder and the oil-reservoir are consequently 


72 


griffin’s oil blast furnace. 

detached, d is a tube which brings oil from the funnel e , 
and / is a tube to be placed in connection with the blowing 
apparatus. The wick-holder contains three concentric wicks, 
placed round the multiple blowpipe c, which is in commu¬ 
nication with the blowing tube. 

The crucible furnace consists of the following parts, 
shown in figs. 30 and 31 :—g is an iron tripod; h is a flue 
for collecting and directing the flame. This flue is of such 
a width, that when the wick-holder, is pushed up into it 
until the top of the wick is level with the top of the clay 
cone, there remains a clear air-space of about g inch all round 


Fig. so. 



between the wick-holder and the cylindrical walls of the 
flue, i represents a fire-clay grate having three tongues, 
shown by i (fig. 32), on its upper surface. These tongues 
support the crucible, without stopping the rising flame. 
k is a fire-clay cylinder which rests upon the grate z, and 
encloses the crucible, forming, in fact, the body of the 
furnace. Of this piece there are three sizes : the smallest is 
of 3 inches bore, and works with crucibles that do not 
exceed 2| inches diameter; a middle size, 4 inches bore, 
for ci ucibles not exceeding inches diameter ; the largest 
size, 5 inches bore, for crucibles not exceeding 4| inches 














































































OIL BLAST FUltXACE. 


73 


diameter. This piece being heavy, is provided with handles, 
as represented in p , fig. 32. The walls of the cylinders 
are from 1 inch to 1^ inch thick. I is a flat plate of fire¬ 
clay with a hole in the centre, used to cover the cylinder k , 
so as to act like a reverberatory dome ; m is a cover which 
prevents loss of heat from the crucible by radiation, but 
gives egress to the gaseous products of the combustion of 
the oil; n is an extinguisher to put over the wick-holder 
when an operation is ended; and o is a support for the 
wick-holder. No chimney is required. 

Management op the Oil-lamp Furnace.— The apparatus is 
to be arranged for use as it is represented by fig. 30. The 


Fig. 31. 



cylinder, k , is to be selected to fit the crucibles, and the 
crucible of a size to suit the quantity of metal that is to be 
melted : 1 lb. of iron requires the smallest of the three cylin¬ 
ders, described above; 1^ lb. the middle size ; 5 lbs. the 
largest size. The air-way between the crucible and the 
inner walls of the cylinder should never exceed \ inch nor 
be less than inch. 

The cotton wicks must be clean, and be trimmed a little 
below the level of the blowpipe c. It properly managed, 
they do not readily burn away, but can be used for several 
fusions. The reservoir should be filled with oil for each 


















































































74 


DETAILS OF MANAGEMENT OF THE 


operation. The proper sort of oil for use is the more volatile 
kind of mineral oil, of the specific gravity of 750, which is 
now easily procurable at about three shillings per gallon. 
The variety known by the commercial name of turpenzine 
answers well. The combustion of a quart of this oil, costing 
ninepence, gives heat sufficient to melt 5 lbs. of cast iron. 
Probably the lighter kinds of paraffin oil may be suitable. 
Liquids of the alcohol class, spirits of wine, and pyroxylic 
spirit can be used; but they are less effective and more 
expensive than turpenzine. Care must be taken not to spill 
the oil on the table or floor, and not to decant it carelessly 
in the neighbourhood of a light, because atmospheric air 
strongly charged with the vapour of these light oils is explo¬ 
sive. When the oil is burnt in the furnace in the manner 
described below, there is no danger. During an operation, 
a wooden screen, as represented by the dotted lines in fig. 
30, should be placed between the oil-reservoir and the furnace, 
to prevent the vaporisation of the oil by radiant heat. As 
the wick-holder 5, and siqqfly pipe d , contain only about 
one fluid ounce of oil, the oil must run continuously during a 
fusion, from the reservoir a into the funnel e , in order that 
the cotton may be always flooded. The success of the 
fusion depends upon the due supply of oil, to which point 
the operator must pay attention. At the commencement of 
a fusion, the oil must be run from the reservoir until the 
surface of the oil in the funnel has a diameter of about an 
inch. The wicks will then be flooded, and a light may be 
applied, and a gentle blast of air then set on. The oil im¬ 
mediately sinks in the funnel, and the stop-cock must be 
opened and so regulated as to keep the oil barely visible at 
the bottom of the funnel. If too much oil is supplied it im¬ 
mediately rises in the funnel, and simultaneously overflows 
the wick-holder. Too much vapour is then thrown into the 
furnace, and the heat is immediately lowered, especially at 
the beginning of an operation, before the fire-clay portions 
of the furnace are well heated. If, on the contrary, too little 
oil is supplied, the wicks burn, and the operation is spoilt. 
The demand of the wick-holder for oil depends upon the con¬ 
dition of the furnace and the character of the fusion in pro- 


OIL BLAST FURNACE. 


75 


gress. When the lamp is newly lighted and the furnace cold, 
the oil should be passed slowly in distinct drops; but as the 
furnace becomes heated the rapidity of the supply of drops 
should be increased; and finally, when the furnace is at a 
white heat, the oil should be supplied in a thin continuous 
stream. When the fusion to be effected is that of only a 
small quantity of metal, such as 1 lb. of iron, a rapid supply 
of drops of oil is sufficient even to the close of the operation. 
At that rate the burner consumes about 1-| pint of oil in an 
hour. When the fusion to be effected is that 4 lbs. or 5 lbs. 
of iron and the large furnace is in action and has been 
brought to a white heat, the supply of oil must, as stated 
above, be in a thin continuous stream, and the operation will 
then consume two pints of oil in the hour. And here it 
requires remark that, with that continuous supply, when the 
furnace is large and is at a white heat, the oil does not rise 
in the funnel, being instantaneously converted into gas at 
the mouth of the burner, and thrown up in that state into 
the furnace for combustion. The operation, indeed, consists 
at that point of a rapid distillation of oil-gas, which is im¬ 
mediately burnt, in the presence of air supplied at a suitable 
pressure by a dozen blowpipes, in effective contact with the 
crucible to be heated. 

The flame produced in this furnace is as clear as that 
produced by an explosive mixture of air and coal-gas. It is 
perfectly free from smoke, and the consumed vapours which 
occasionally escape with gaseous products of the combustion, 
are even less unpleasant to smell and to breathe in than 
are those which are usually disengaged by a blast gas 
furnace, or by an ordinary lamp, fed with pyroxylic spirit. 

The contents of a crucible under ignition in this furnace 
can at any moment be readily examined, it being only 
necessary to remove the pieces l and m with tongs, and to 
lift the cover of the crucible, during which the action of the 
furnace need not be interrupted. 

When the operation is finished, the blast is stopped, the 
stop-cock is turned off, the oil-reservoir is removed, the 
wick-holder is lowered on the support c, withdrawn from 
the furnace, and covered with the extinguisher n. The 


76 


POWER OF TIIE FURNACE. 


quantity of oil which then remains in the lamp is about one 
fluid ounce. 

Power of the Oil-lamp Furnace. —The furnace being cold 
when an operation is commenced, it will melt 1 lb. of cast 
iron in 25 minutes, 1^ lb. in 30 minutes, 4 lbs. in 45 minutes, 
and 5 lbs. in GO minutes. When the furnace is hot, such 
fusions can be effected in much less time; for example, 1 lb. 
of iron in 15 minutes. It need scarcely be added, that small 
quantities of gold, silver, copper, brass, German silver, &c., 
can be melted with great ease, and that all the metallurgical 
and chemical processes that are commonly effected in pla¬ 
tinum and porcelain crucibles can be promptly accomplished 
in the smallest cylinder of this furnace ; and in the case of 
platinum vessels, with this special advantage, that the oil¬ 
gas is free from those sulphurous compounds the presence of 
which in coal-gas frequently causes damage to the crucibles. 

Requisite Blowing Power. —The size of the blowing- 
machine required to develop the fusing power of this oil-lamp 
furnace depends upon the amount of heat required or the 
weight of metal that is to be fused. For ordinary chemical 
operations with platinum and porcelain crucibles, and even 
for the fusion of 1 lb. of cast iron in clay or plumbago cru¬ 
cibles, a blowing power equal to that of a glass-blower’s 
table is sufficient, provided the blast it gives is uniform and 
constant. But the fusion of masses of iron weighing 4 or 
5 lbs. can be effected by the gas which this oil-lamp is ca¬ 
pable of supplying, provided a sufficiently powerful blowing- 
machine supplies the requisite quantity of air. When more 
than a quart of oil is to be rapidly distilled into gas, and the 
whole of that gas is to be instantly burned with oxygen, it is 
evident that effective work demands a large and prompt 
supply of air. 

As in all practical matters of this sort, the cost is a main 
question, it may be useful to state that the price of this 
apparatus complete, without the blowing-machine, but in¬ 
cluding every other portion necessary for heating crucibles 
up to the size sufficient to fuse 1 lb. of cast iron, is one guinea; 
and that, with the extra furnace pieces for crucibles suitable 
for 5 lbs. of iron, or any intermediate quantity, the cost is 
one guinea and a half. 


griffin’s gas blast furnace. 


77 


Gas Blast Furnace.— The furnace (shown at fig. 33) is 
suitable for the fusion of refractory metals, and for all 
purposes of ignition, combustion, fusion, or dry distillation 
at a led or a white heat, where it is desirable to produce 
those temperatures and effects promptly, steadily, and con¬ 
veniently. This furnace has also been devised by Mr. Griffin. 


Fig. 33. 



It consists of two parts : firstly, of a particular form of gas- 
burner, which is supplied with gas at the usual pressure, 
and with a blast of common air, supplied with bellows or a 
blowing-machine, at about ten times the pressure at which the 


Fig. 34. 



gas is supplied; secondly, of a furnace which is built up round 
the flame that is produced by the gas-burner, and the crucible 
that is exposed to ignition. The object of the peculiar con¬ 
struction of this furnace is to accumulate and concentrate to 
a focus the heat produced by the gas-flame, and to make it 
expend its entire power upon any object placed in that focus. 


























































78 


GAS BLAST FURNACE. 


The gas-burner is a cylindrical iron reservoir, constructed 
as shown in fig. 34, which is drawn on a scale of one-third 
the full size. It contains two chambers, which are not in 
communication with one another. Into the upper chamber, 
gas at ordinary pressure is allowed to pass by the tube 
marked gas. Into the lower chamber, air is forced by the 
tube marked air. The upper part of the burner is an inch 
thick in the metal. Through this solid roof holes are bored 
for the escape of the gas. The experiments described here¬ 
after were chiefly made with a burner that contained sixteen 
holes, arranged as shown in fig. 35, which is a surface view 
of the burner represented by fig. 34. But burners with 
three holes, six holes, and twenty-six holes, have been made 
for other purposes. The number of holes depends, of course, 
upon the heating power required from the burners. The 
air passes from the lower chamber, through a series of metal 
tubes placed in the centre of the gas-holes, and continued to 
the surface of the burner, so that the gas and air do not mix 
until both have left the gas-burner, and then a current of air 
is blown through the middle of each jet of gas. The bottom 
of the gas-burner is made to unscrew, and the division be¬ 
tween the two chambers which carries the air-tubes is easily 
removable for the purpose of being cleaned. The gas and 
air pipes are both half an inch in the bore, and may be 
about ten inches long ; the gas should have a pressure of 
half an inch of water, and the blast of air about ten times 
that pressure. The quantity of gas used in an hour is about 
100 cubic feet. The stop-cock which supplies it has a bore 
of half an inch. The round rod which is represented at the 
bottom of the burner, fig. 34, is intended to fit it to the 
support, shown by 5, in figs. 36 and 41. 

When the gas is lighted and the blast of air is put on, the 
flame produced by the gas-burner is quite blue and free from 
smoke. It is two inches in diameter, and three inches high, 
and the point of greatest heat is about two inches above 
the flat face of the gas-burner. Above tins steady blue 
flame there rises a flickering ragged flame, several inches in 
height, varying with the pressure of the gas. In the blue 
flame thin platinum wires fuse readily. 


GAS BLAST FURNACE. 


79 


When the gas is burning in this manner, and the appara¬ 
tus is attached to flexible tubes, the burner may be inverted 
or held sideways, without disturbing the force or regularity 
of the flame, so that the flame may be directed into a furnace 
at the bottom, the top, or the side, as circumstances may 
require. 

The following articles are used in building up the gas 
furnace for different experiments. They vary in size ac¬ 
cording to the volume of the crucible, or the weight of the 
metal which is to be heated. 

A circular plate of fire-clay, two inches thick, with a hole 
in the centre, exactly filling the upper part of the gas-burner, 
which is made to enter into the hole three-quarters of an 
inch. In external diameter this clay plate agrees with each 
size of furnace. 

A cylinder of fire-clay, of which two pieces are required 
to constitute the body of each furnace. In the middle of 
each cylinder a trial-hole is made, one inch in diameter, to 
which a fire-clay stopper is adapted. (See fig. 36.) 

A fire-clay cylinder, closed at one end, and pierced at the 
open end with numerous holes of half an inch in diameter. 
The thickness of the clay is immaterial. There are several 
sizes of this cylinder for crucibles of different diameters. It 
is represented at a, fig. 37. 

A circular plate of fire-clay from two to four inches in 
diameter, and one inch thick. Similar pieces half-inch thick 
are useful. 

Cylinders of plumbago, pierced with numerous holes of 
three-eighths of an inch in diameter. Their use is to support 
flanged crucibles over the flame. 

A cover or thin plate of plumbago, three inches in dia¬ 
meter. It has a small hole in the middle, and being of a 
soft material, the hole can be easily cut or filed to suit cru¬ 
cibles of any desired size, so as to support them on the 
cylinder. 

As in all cases the heating power of the gas furnace spreads 
laterally, and does not rise vertically, the most advisable form 
of the crucibles required for use in it is short and broad , not 
tall and narrow, and the supporting cylinders must be shaped 


80 MODIFICATIONS OF GAS FURNACE. 

accordingly. No fire-bars or grates can be used to support 
crucibles in this gas-furnace, because no material, formed 
into narrow bars, can sufficiently withstand its powers of 
fusion and combustion. 

A plumbago cylinder, or crucible-jacket, two and a half 
inches high, two and a-half inches in diameter, and a quarter 
of an inch thick in the walls. It has several holes of three- 
eighths of an inch in diameter. 

A circular cover or dome, flanged at the bottom, and 
having a knob or handle at the top. It is pierced with 
twenty-four holes of a quarter of an inch in diameter, arranged 
in two rows near the bottom. This dome, when of small 
size, is made of plumbago ; when of large size, of fire-clay. 

Plumbago crucibles made with a flange or solid over¬ 
hanging rim, the use of which is to suspend the crucibles 
over the gas-burner, by means of the cylinders. When the 
crucibles are too small to fit the cylinders, a flat plate is 
filed to fit the crucible, and is then placed on the cylinder, to 
the diameter of which it is adapted. 

Besides these pieces of fire-clay and plumbago, it is neces¬ 
sary to be provided with a strong iron tripod, to sustain 
the furnace, as represented by c in fig. 36, an iron pan in 
which to place the furnace, and a quantity of gravel or 
rounded flints, not less than half an inch, nor more than one 
inch in diameter. These pebbles form an essential part of 
this gas furnace. 

Gas Furnace arranged for Heating at the Top. —This 

gas furnace is exhibited in section by fig. 36 : a is the gas- 
burner ; b is the support for it when used below the furnace ; 
c is the iron tripod support for the furnace ; d , d, are two 
perforated clay plates adapted to the gas-burner a ; 0 , e , are 
two clay cylinders. These pieces, a to 0 , are similar in all 
the furnaces, and will not require description in each 
example. 

The interior of the furnace, as represented by fig. 36, is 
built up as follows :—The clay plate, d , is put upon the 
tripod, c. Over the central hole in d the clay cylinder is 
placed, and upon that cylinder, two or three of the clay 
plates. Upon these a porcelain or platinum crucible is 


GAS BLAST FURNACE. 


81 


placed. If it is of platinum, a piece of platinum foil maybe 
put between the crucible and the uppermost clay plate, to 
protect the crucible from contact with particles of iron, or 
against cementation to the clay. The crucible is to be sur¬ 
rounded by the plumbago jacket. The space between this 
pile in the centre of the furnace and the two cylinders, e, e, 
which form the walls of the furnace, is to be filled with flint- 
stones or gravel, washed clean and dried. The stones which 
answer best are rounded, water-worn pebbles, of half an inch 
to one inch diameter. These may be piled up to the top 
edge of the jacket. 


Fig. 36. 


Fig. 37. 


Fig. 38. 




Fig. 39. 





Fig. 40. 


It has been found convenient to give the crucible jacket a 
conical form, the better to adapt it to the usual shape of the 
crucible. The four figures, 37, 38, 39, 40, show the method 
of using it so as to make crucibles of different sizes fit the 
furnace properly. 

In these figures a represents a ventilator or hollow support, 

G 





























































































































82 GAS BLAST FURNACE. 

the sides of which are pierced full of holes. This is placed 
over the hole in the lower nozzle plate, to permit of the 
descent and escape of the carbonic acid gas and steam 
produced by the combustion of the gas in the furnace: b 
represents a cone open at both ends and pierced full of holes. 
Its use is to contain the crucible that is to be exposed to heat, 
as represented by d in figs. 39, 40, 41. 

The ventilator and cone together should be equal, or 
nearly equal, to the height of the body of the furnace: the 
top of the crucible should be about 2^ inches from the fiat 
iron face of the gas-burner, that being in general the place 
of greatest heat, but this is subject to a variation of inch 
more or less, according to the supply of gas. The space 
between the crucible and cone should be about ^ inch ; if 
much wider the heating power of the furnace is diminished. 
The space between the ventilator and cone, a, b , and the 
sides of the furnace, must be completely filled by flints of 
from \ inch to 1 inch diameter. When the flints split 
up, the powder produced must be occasionally removed, 
as it stops the draught of the furnace. In order to 
raise the crucible to the proper distance from the face of 
the burner, round clay plates are used : thus, c (fig. 39) 
shows how to raise a crucible within a cone; and c (fig. 40) 
shows how a small cone can be raised above the ventilator 
to the proper height. Different sizes of cones may be used 
in the same furnace, the cone being chosen in each opera¬ 
tion to fit the crucible, the quantity of surrounding pebbles 
being of no consequence, provided the furnace is filled up 
to the edge of the cone. 

The Process of Fusion —The apparatus being thus ar¬ 
ranged, the gas is to be turned on, and lighted; the blow¬ 
ing machine is then to be put into action, and the nozzle 
of the gas-burner depressed into the central hole of the 
clay plate <f, as shown in fig. 36. The whole force of 
the blue flame then strikes the crucible; part of it forces its 
way through the holes in the cone or crucible jacket, and part 
of it rises and passes over the upper edge of the jacket; after 
which it finds its way downwards between the pebbles. 
The carbonic acid gas and the vapour of water which 


FUSION IN TIIE GAS FURNACE. 


83 


result from the combustion of the'gas, together with the 
nitrogen ot the air and any uncombined oxygen, accompany 
it. No space being left open for the escape of these gases at 
the upper end of the furnace, they go downwards through 
the interstices among the pebbles, and passing through the 
holes in the ventilator a (fig. 37), and through the central 
hole in the lower plate a (fig. 3G), they escape finally into 
the air. In this progress, the hot gases give up nearly all 
their heat to the flint stones. Water and gases escape 
below at a very moderate temperature : water even runs 
down in the liquid state, while the stones rapidly acquire a 
white heat, and if the blast and the supply of gas are con¬ 
tinued they retain that white heat for any desired length of 
time—for hours. 

Precautions to be observed on commencing a Fusion.— 

When a furnace and its contents are cold, and a burner is 
newly lighted, it must not be suddenly plunged into the 
furnace, and the full heat be applied at once ; otherwise the 
fire is apt to go out, or the crucibles and interior fittings to 
crack from the too sudden application of a violent heat. It 
is better to let the flame play a little time into the opening of 
the furnace, before the burner is thrust closely into its place. 
The crucibles and furnace fittings should be quite dry when 
used. It is recommended, after arranging a furnace for a 
fusion, first to warm it by a large gas-burner, before apply¬ 
ing the blast-burner. When the furnace has been warmed 
the full heat may then be applied safely. At the end of ten 
minutes after lighting the gas, the crucible, placed in the 
described circumstances and exposed to the full action of 
the heat of the gas, and surrounded by substances which 
are bad conductors of heat, is raised, with the jacket and 
pebbles around it, to a white heat. The consequence is that 
the full power of the gas jet is then exerted upon the 
crucible and its contents, and those effects are produced 
which will be described presently. 

If it is desired to inspect the substance subjected to the 
action of heat in this furnace, the gas-burner is lifted out, 
and the crucible is examined through the hole in the clay 



84 


POWER OF THE GAS FURNACE. 


plate. To make it possible to inspect substances at a white 
heat, the view is taken through a piece of dark cobalt 
blue glass. If the substances submitted to heat suffer 
no harm from the action of oxygen, it is better to dis¬ 
pense with a crucible cover and to direct the jet of flame 
directly down upon the substance to be heated. The action 
is then more rapid. When the burner is taken out, the 
substance in the crucible can be stirred, if it is considered 
necessary. 

Results. —The following experiments will give an idea 
of the power of a furnace of this description. A common 
clay crucible, 3 inches high and 3 inches diameter at the 
mouth, was filled with about 24 ounces of cast iron. It 
was mounted like fig. 3G in a furnace of 4 inches internal 
diameter and 8 inches deep. The pebbles were filled in to 
the edge of the crucible. No crucible cover and no jacket 
were used. The flame was thrown directly upon the iron. 
In a short time the iron melted; the oxygen then converted 
some of the cast iron into magnetic oxide of iron, which 
formed a thin infusible mass on the surface of the cast iron. 
At twenty minutes from the lighting of the gas, the furnace 
was dismounted. The crucible was taken out. A hole 
was broken by an iron rod in the infusible surface of oxi¬ 
dised iron, and the fused cast iron below it was decanted 
into a mould, and made a clear casting weighing 20 ounces. 
In the same small furnace 32 ounces of copper were fused 
in fifteen minutes. When the furnace is hot, that quantity 
of copper or cast iron can be fused in ten minutes. In a 
furnace of the same dimensions, but with a gas-burner 
having only six instead of sixteen jets, 16 ounces of copper 
or of cast iron can be completely fused in ten minutes, 
if the furnace is cold, and in seven minutes if the furnace 
is hot. 

These experiments show that within twenty minutes a 
heat is producible in this little furnace which is more than 
sufficient for most assaying or metallurgical operations. 

Gas Furnace heated at the Bottom.— This is exhibited in 
section by fig. 41. 

In this furnace the parts marked a , b, c, d, e, e, are the 


FUSION IN THE GAS FURNACE. 


85 


same as those similarly marked in fig. 3G ; but the gas-burner 
is in this case put into the bottom of the furnace, instead of 
the top, and the arrangement of the crucible and its support 
is altered in the manner shown by the figure. Upon the 
centre of the clay-plate, d, the perforated plumbago cylinder 
is placed, and upon that a plumbago crucible. These are 
placed together in position in fig. 41. The size of the 
crucible and the height of the 
perforated cylinder are to be so 
adjusted that the bottom of the 
crucible shall be struck by the 
hottest part of the gas flame : that 
is to say, the space left between 
the face of the gas-burner and the 
bottom of the crucible must not 
exceed 2| inches. The crucible is 
provided with a closely-fitting 
cover, and pebbles are then filled 
in between the crucible jacket and 
the furnace cylinder 0 , and are 
covered over the crucible until both 
the pieces of the furnace, e e 9 are 
nearly filled. The gas is then 
lighted, the blast of air is set on, the gas-burner is forced up 
into the hole in the clay plate d , and the operation proceeds. 
In from ten to twenty minutes after the gas is lighted—this 
difference of time depending upon the size 01 the furnace 
and the weight of metal contained in the crucible—the 
interior of the lower cylinder e acquires a white heat. The 
progress of the operation can be watched by occasionally 
removing the stone peg in the trial-hole of the furnace 
cylinder e. The heat very slowly ascends into the upper 
cylinder, and it never becomes so great in the upper as in 
the lower cylinder. The greatest fusing power of the fur¬ 
nace is confined within a vertical space of about 6 inches, 
reckoning from the bottom. The power of flint pebbles 
to abstract heat from the gases which pass through this 
apparatus is quite remarkable. When about 6 inches of 
pebbles lie above the crucible, and the crucible and the 







































8G 


rOWER OF THE GAS FURNACE. 


pebbles about it have been white-hot for half an hour, the 
hand can be held over the top of the furnace within a few 
inches of the pebbles without inconvenience. It becomes 
wetted with the vapour which rises from the furnace, but 
feels only a moderate degree of heat. 

This form of the furnace is attended by the inconvenience 
that we cannot examine the condition of the matter con¬ 
tained in the crucible, to ascertain when the heat has been 
continued long enough. In cases where the fusion is per¬ 
formed repeatedly on the same weight of metal, this would 
be of no importance, because the power of the furnace is 
so steady and regular that the time of firing which has 
been found to answer once will answer the same purpose 
again. 

When it is supposed that the fusion of the metal submitted 
to trial is comjffeted, the gas is first to be turned off, and 
then the supply of air stopped. We can either allow the 
furnace to remain intact till it is cold, or lift off the cylinders 
e e with tongs, and allow the hot stones to fall into the 
iron pan placed below the furnace to receive them. A few 
bricks should be laid between the pan and the table or stool 
on which it rests, if the latter is made of wood, because the 
heat given off by the pebbles is very great. The pebbles 
being raked away from the crucible, the contents of the 
latter can be examined. 

The absolute sizes of the furnaces depend upon the 
amount of work required from them. The fusions described 
below were mostly made in a furnace of 6 inches internal 
diameter, a few in a furnace of 4 inches internal diameter 
and one or two in a furnace of 8 inches internal dia¬ 
meter ; all of them with a gas-burner of 16 holes and a 
supply of gas obtained from a J^-inch pipe. A large furnace 
with an internal diameter of 12 inches, will demand a 
gas-burner of 26 holes, and a supply of gas from a pipe 
of nearly 1 inch in the bore. 

Examples or Fusion effected by the Blast Gas Furnace.— 

The fusing points of certain metals have been fixed by 
Daniell at the following temperatures :— 


CRUCIBLES FOR GAS FURNACE 


87 


Silver 

Gold 


1873 Copper 

2016 Cast-iron 


1996 

2786 


Brass, with 25 per cent, of zinc, at 1750° F. 


All these metals melt readily in the gas furnace. Quanti¬ 
ties of 3lbs. of copper or cast iron can be completely fused in 
fifteen minutes in a 6-inch furnace. Quantities of 8 lbs. or 
10 lbs. of copper or cast iron can be completely fused into a 
homogeneous mass in a 6-inch or 8-inch furnace within one 
hour, using a 16-hole burner, and a supply of gas from a 
^ inch pipe. 

In a furnace of the same size 45 ounces of nickel have 
been fused, and in other experiments masses of wrought 
iron, weighing 18 ounces, 28 ounces, and 40 ounces, have 
been produced. The piece of 18 ounces was perfectly fused. 
The piece of 40 ounces was not quite fused, the crucible 
having melted and stopped the operation. Cobalt has also 
been fused, and reduced to the metallic state from the 
peroxide by ignition with charcoal. The time required for 
the fusion of these refractory metals is from one and a half 
to two hours. 

Scraps of platinum can be fused into a porous mass, but 
not into a solid homogeneous bead. Thin platinum wires 
fuse readily in the free flame of the gas-jet produced by the 
burner fig. 34; but when the jet plays upon a quantity of 
the metal contained in a crucible, the relations of power and 
effect are different. 

When the metals to be melted are such as do not undergo 
oxidation, the method of action represented by fig. 36 is 
most convenient. In this manner gold can be readily 
melted, and by removing the gas-burner the melted metal 
can be stirred. When the action of oxygen is to be 
avoided, the crucible must have a cover, which in some cases 
should be securely luted to it. 

Choice or Crucibles. —The experiments above referred to 
were made with coal gas at the ordinary pressure, and with 
a blast of cold atmospheric air. Greater effects can be 
produced by the use of oxygen gas, or of heated atmospheric 
air. But a difficulty stands in the way of the use of these 



88 


GAS MUFFLE FURNACE. 


greater degrees of heat in the want of crucibles capable of 
enduring their action. 

With cold atmospheric air, pure nickel and pure iron 
attack every kind of siliceous crucible, and it is therefore 
needless to heat the air or to prepare oxygen till a superior 
kind of crucible is obtainable. At present, these metals 
can only be melted in plumbago crucibles, which necessarily 
communicate to them more or less carbon. Metals which 
melt at moderate degrees of heat, such as gold and copper, 
are easily fused either in clay crucibles or in those of plum¬ 
bago—the latter, be it remembered, being a mixture of gra¬ 
phite and clay. Metals in combination, sucli as cast iron, 
also melt readily in clay crucibles without destroying them. 
But when such metals as iron, nickel, and cobalt, are freed 
from carbon, and brought into a state of purity, they 
acquire an extraordinary attraction for silica at a white 
heat, so that the metal and the silica readily run down 
into a very fusible silicate. Even when plumbago crucibles 
are used, the carbon burns away at some particular point; 
the metal then attacks the clay, bores a hole through the 
crucible, and finishes the operation. 

No kind of clay or porcelain will withstand the action of 
pure iron or nickel at a white heat; it is therefore almost 
impossible to effect any large fusions of these metals when 
they are free from carbon. 

Fusion of Metals in large quantities, and Ignition of 
Objects of large size —As the gas-burner fig. 34 can be 
held in any required position, it is possible to apply heat to 
large objects by using several gas-burners. Thus a large 
crucible may be fixed in a square furnace, and gas-burners 
be applied below and on the four sides of the furnace, the 
spaces between the crucible and the walls of the furnace 
being filled with pebbles, to collect the heat and apply it to 
all parts of the crucible. 

Muffle Furnace for Assaying, Roasting, etc.— A muffle 
placed in an assay furnace, and built up with pebbles, can 
be heated either from above or from below by the blast 
gas-burner. The flame and products of combustion can be 
made to sweep through the muffle, whether going upwards 


89 


USES OF THE GAS FURNACE. 

or downwards. The air-pipe and yas-pipe attached to the 
gas-burner (fig. 34) must each be provided with a stop-cock. 
W hen the front door of the muffle is opened to afford the 
opportunity for examining the cupels, the blast, if continued, 
'would blow these out against the operator, but that occur¬ 
rence is prevented by turning the stop-cocks. When it is 
desired to oxidise the substances in the muffle, the furnace 
is first brought up to a sufficient temperature, and then the 
gas is turned off, but the blast of air is continued. The air 
passing through the hot pebbles enters the muffle at a high 
temperature, and not exhausted of oxygen, because there is 
no carbonaceous matter present among the pebbles when 
the gas is turned off. The pure and highly-heated air 
is consequently in a proper position for oxidising metals 
that are already raised to a red heat in the muffle. The 
same apparatus is useful where substances require to be 
roasted in the presence of air in order to oxidise and expel 
some volatile ingredient. We have in this process an 
effectual means of using hot air to aid the process of cupel- 
lation. 

Miscellaneous uses of the Blast Gas Furnace. —1. The 

preparation of chemical substances by the projection of 
mixtures into a crucible kept at a red or a white heat. 

2. For melting silver, gold, copper, cast iron, brass, bronze, 
nickel-silver, &c., either for making small castings or ingots. 

3. For experiments on glass, every description of which it 
is able to fuse. 4. For experiments on enamels, coloured 
glasses, and artificial gems. 5. For experiments on metallic 
alloys. 6. For the fusion of steel. 7. For the use of 
dentists, in the preparation of mineral artificial teeth. 
8. For the assay of ores of silver, copper, lead, tin, iron, and 
other metals. 9. For all purposes of ignition, combustion, 
fusion, or dry distillation, at a red heat or a white heat, 
where it is desirable to produce those temperatures promptly 
and cheaply. 

Repair of the Gas Furnace.— When the clay cylinders 
become warped or chipped, so as to allow the gases to 
escape at the joints laterally, they must be luted for each 
operation by applying a little wet fire-clay by means of a 


yO MINATURE BLAST GAS FURNACE. 

spatula, ^hen only a moderate heat is required, this 
luting is unnecessary. 

Many chemical ignitions performed on small quantities 
of substances in analytical processes, demand a degree of 
heat greater than that afforded by gas-burners with draught, 
but not so much as is supplied by the powerful blast¬ 
furnaces described in the preceding section. Mr. Griffin 
has therefore described an apparatus intended to meet this 
requirement. It will readily raise to a white heat all the 
sizes of platinum and porcelain crucibles that are commonly 
in use, and such sizes of clay or plumbago crucibles as will 
contain a pound of cast iron, which quantity of metal this 
furnace will melt. Figs. 42, 43, 44, represent three ex¬ 
amples of the miniature blast furnace. This consists, in the 
main, of a blast gas-burner, similar in construction to that 
represented by fig. 34, but smaller in size, and having only 
three jets. It is fixed upon, and forms part of, the furnace 
support, as represented in the figures. Upon the iron 
nozzle of the burner there is fixed a fire-clay nozzle-plate 
or furnace-sole, similar to cl (fig. 36), and upon this plate 
the little furnace is built up of loose clay cylinders, which 
are in all cases selected to suit the size of the crucible 
that is to be operated upon. The entire furnace rests on 
the solid shoulder of the gas-burner. No pebbles are used, 
the degree of heat that is intended to be raised not requiring 
their aid. . Gas supplied at common pressure by a l-inch 
pipe is sufficient. 

In mounting this furnace, it is necessary to place between 
the nozzle-plate or sole, and the conical flue placed upon it, 
three small feet, to separate the two pieces, and give room 
for the influx of atmospheric air around the flame, without 
which the proper heat of the furnace is not obtained. 
Three bronze halfpenny pieces answer the purpose exactly. 

Upon comparing the three figures it will be perceived 
that the interior of the furnace is exactly alike up to 
the grate or trivet, and differs above that only in having 
cylinders that suit the different sizes of crucibles that are to 
be heated. 

It is in the power of the operator, when working with 


gore’s gas furxace. 


91 


platinum crucibles, to dispense with the grate and to hang 
his ci liable in the hottest part of the furnace by a sling of 
platinum wire suspended from an iron bar laid across the 
top of the furnace. The piece marked u (in fig. 42) being 
omitted, the two pieces e e come together and form a cavity, 
in the centie of which the crucible is to be suspended. If 
it then appears to be too low in the flame, the height can be 
laised by putting such pieces as a or c (fig. 54) between the 
lower piece e and the sole. For the above description, and 

many of the cuts, we are indebted to the kindness of Mr. 
Griffin. 

G. Gore, Esq., F.E.S., has devised a gas furnace which 


Fig. 44. 


Fig. 43. 


Fig. 42. 





will fuse cast iron, &c., and still allow the melted substances 
to be perfectly accessible to be manipulated upon for a con¬ 
tinuous and lengthened period of time, without contact with 
impurities or with the atmosphere, and without lowering 
their temperature sufficient to cause them to solidify. These 
conditions Mr. Gore has obtained by means of ordinary 
coal-gas and atmospheric air, without the use of a bellows 
or lofty chimney, or of regenerators or valves requiring fre¬ 
quent attention. The arrangement is as follows : A (figs. 45 
and 46) is a cylinder of fire-clay about nine inches high 
and six inches diameter, open at both ends, with a hole in 
its side near the bottom to lead into the chimney; it is 




































































92 


gore’s GAS FURNACE. 


covered by a movable plate of fire-clay, i>, with a hole in 
its centre for introduction or removal of the crucible, &c.; 
this hole is closed by a perforated plug of clay 6 y , for access 
to the contents of the crucible, and that again is closed by 
another clay stopper I) : E is a chimney of sheet iron about 
five or six feet high, kept upright by a ring of iron F 
attached to the top of the furnace. The fire-clay cylinder 
is closed in a sheet iron casing with a bottom of iron, to 
which are fixed three iron legs G. An iron tube //, with a 

Fig. 45. Fig. 46. 



prolongation /, supports by means of the screw J the 
burner K and its tube Z, which is open at both ends. Gas 
is supplied to the burner by means of the tap M , which has 
a small index iV attached to it for assistance in adjusting the 
gas. Inside the large cylinder is another fire-clay cylinder 
or cupola 0, with open ends, and with three projections of 
fire-clay P for supporting the crucible Q ; it is kept steady 
by means of three clay wedges B ; S is an air-valve for 
closing the bottom of the tube L. The gas-burner is a thin 








































































































gore’s gas furnace. 


93 


metal cylinder, deeply corrugated at its upper end, with the 
corrugations diminishing to nothing at its lower end, as 
shown in the engravings. The action of this furnace is as 
follows: Gas is admitted to the open tube L by the tap M ; 
it there mixes with air to form a nearly combustible mix¬ 
ture, which ascends through the burner, and burns in the 
clay cylinder 0, being supplied with the remainder of air 
necessary to combustion through the tube II to the outer 
surface of the flame ; the products of combustion pass up 
through cylinder 0, and then downwards outside of it to 
the chimney, the point of greatest heat being at Q. 

It is important in using this furnace that the burner is 
placed quite in the centre of the bottom of the tube 0 ; also 
that a crucible of not too large nor too small dimensions 
be selected. The most suitable way of supporting a smaller 
crucible is by placing it in a larger one that has had its 
upper part broken off. If desirable, a little clay luting may 
be placed round the top edge of the iron casing to exclude 
air entering between it and the cylinder ; also a little thin 
clay luting upon the part of the bottom of the furnace where 
the inner cylinder 0 rests. 

In lighting the furnace, the plugs C and D are removed, 
a light held inside the opening, and the gas turned on full. 
Should the flame blow down to the bottom of the tube L on 
lighting (which, however, rarely occurs unless the furnace is 
already hot), the gas must be turned off, and the bottom of L 
momentarily closed whilst lighting the gas as before. Should 
the flame not burn down to the burner but only burn to the 
orifice in the clay plate B , it must at once be extinguished 
and relighted, otherwise some of the gaseous mixture will 
pass into the chimney unburned, and subsequently ingnite 
and cause an explosion. A large flame now issues from the 
top orifice, and is white if too much gas is on, and chiefly 
violet or red with the proper quantity ; it should now be 
coarsely adjusted until these appearances are represented. 
The annular plug C should now be inserted, which will 
compel it to pass downwards to the chimney, and as soon as 
the small remaining flame now issuing disappears, or nearly 
disappears, as it will in a few seconds, the small stopper D 


94 


gore's GAS FURNACE. 


should also be inserted. In lieu of this, the large dame 
may be dedeeted against the chimney by means of a piece 
of sheet iron until it withdraws inwards as before men¬ 
tioned ; the two plugs may then be reinserted. The gas 
tap may now be partly adjusted. The crucible should be 
placed in the furnace after the act of lighting the gas, but 
not immediately after if the furnace is cold, or explosions 
may occur by unburned gaseous mixture passing the crucible 
into the chimney, and igniting afterwards. 

After about five minutes the gas should be slowly ad¬ 
justed, until a sound is heard inside like a series of small 
explosions. This sound is sometimes not very distinct, 
especially at high temperatures, and therefore requires a 
little experience in the use of the furnace in order to be 
detected. It is, however, a chief guide in determining the 
proper amount of gas, and should therefore be carefully 
studied. To assist in adjusting the gas it will be found 
very useful to place a small piece of looking-glass beneath 
the tubeZ, and to adjust the gas tap until the flame between 
the burner and crucible appears wholly violet or slightly 
white ; but this test is liable to fallacy if employed when the 
gas is first lighted, because the coldness of the parts makes 
the flame much whiter than it otherwise would appear. It 
is also fallacious, the flame appearing whiter than it really 
is when the crucible is very hot. It is, however, of great 
assistance, especially at intermediate temperatures. A 
rough deposit upon the outer edge of the crucible indicates 
an excess of gas ; the deposit is carbon. Less gas is re¬ 
quired with a crucible in the furnace than without one; 
also less is required when the small hole at the top of the 
furnace is open than when it is closed; and less is also 
required when the furnace is cold than after it has been 
lighted some time, because the draught gradually increases 
and draws in more air. After having accurately adjusted 
the gas, no further attention to the furnace is requisite. 

IT iving once found the proper adjustment of gas under 
certain known conditions, it is well to notice the position of 
the index pointer A 7 , in order to be able at once to adjust it 
to about the right point on other occasions. Under ordinary 


95 


gore’s gas furnace. 

circumstances, during daylight it is best to set the gas nearly 
full on at first, and fully on at about live minutes afterwards 
when the draft has become more powerful; but during 
twilight, when the supply ot gas from the gas works is more 
free, the index pointer may be set at the numbers 2i or 3. 
The gas should be supplied by a pipe of not less than f-inch 
bore, with a main pipe of ^ an inch; but all depends 
upon the pressure of gas at the particular locality, which is 
very variable. The consumption of gas varies from 30 to 40 
cubic feet per hour, the value of which is about twopence. 

The top of the chimney should be placed in a position 
where the products of combustion can pass freely away. If 
it is placed in an opening or pipe leading to another chimney, 
care must be taken not to have the draught too powerful, 
otherwise the heat will be drawn more into the chimney, 
and the supply of gas in the daytime may be found rather 
deficient. The furnace will act satisfactorily, though less 
powerfully, with the chimney standing in an open room 
without any special outlet for the products of combustion, 
provided the full height (6 feet) of chimney is employed. 
Under other circumstances a chimney 4^ or 5 feet high may 
be used. 

This furnace will produce what is generally called a white 
heat; it will readily melt half a pound of copper, or six 
ounces of cast iron; it will melt as large a quantity of those 
substances as the largest sized crucible that can be introduced 
into it will contain, sufficient space being reserved around 
the crucible for draught. It requires from 20 to 30 minutes 
to acquire its highest temperature, and then the entrance part 
of the chimney exhibits a faint red heat in daylight. If it 
exhibits much more than this the draught is too powerful, 
and if less, there is not sufficient gas. 

With one ounce of copper put into the cold furnace, and 
the gas lighted and properly adjusted, the copper generally 
begins to melt at about the tenth or twelfth minute, and is 
completely melted by the fifteenth. With the heat well up, 
1 ounce of copper has been melted in it in 2^ minutes, 
1 ounce of cast iron in 3 minutes, 5 ounces of copper 
in 4| minutes, and 3 ounces of cast iron in 5 minutes. 


9G GRIFFIN’S REVERBERATORY GAS FURNACE. 

With the smaller hole in the top of the furnace open, 1 
ounce of copper lias been melted in 3i minutes, and several 
ounces of copper have been kept in fusion upwards of half 
an hour, and may be kept so for any length of time; cast 
iron has also been fused, and kept melted under the same 
conditions. These various effects have also been obtained 
in a somewhat diminished degree with the chimney standing 
in an open room. 

When the small hole D is open some air is drawn in that 
way, and less air passes up with the gas through the tube (9, 
but the cold air does not much diminish the temperature of 
the crucible, because it combines with the excess of gas now 
passing over the edge of the inner cylinder; it, however, 
renders the flame round the crucible white by deficiency of 
air, and this should be partly corrected by lessening the gas. 
An excess of either gas or air renders the surface of melted 
copper dull. 

When it is desirable to perfectly avoid contact of air with 
the fused substance during manipulation, a narrow crucible 
should be employed, and a thin narrow ring of fire-clay 
should be placed upon the top of the tube 0 to contract its 
opening ; the flame then closes completely over the top of the 
crucible and prevents access of air ; a proper adjustment of 
gas, together with exclusion of air in this manner, enables a 
perfectly bright surface of melted copper, or even tin, to be 
continuously maintained, from which the images of parts 
above are clearly reflected. The clay ring may be with¬ 
drawn by lifting the plate B. A less perfect exclusion of air 
may be obtained by employing a narrow crucible placed 
rather low down in its support. A small iron dish should 
be placed beneath the tube Z, to receive any melted substance 
that may fall. The chief conditions of success in the use of 
this furnace are sufficient gas, a suitable degree of draught, 
and proper regulation of gas to air. 

The advantage which Mr. Gore’s gas furnace possesses 
over those previously described is that no artificial blast is 
required in using it. Mr. Griffin has since devised what he 
calls a Reverberatory Gas Furnace , which also produces a 
high temperature without the use of a blowing machine. It 


Reverberatory gas furnace. 


07 


is especially suitable for assay purposes on a small scale and 
for the decomposition of siliceous minerals by fusion with 
alkaline carbonates in platinum crucibles, being capable of 
fusing 1,000 grains of anhydrous carbonate of soda in ten 
minutes. 

The different parts of this furnace are also arranged in a 
very convenient manner, so as to admit of its being employed 
for purposes in a chemical or assay laboratory. It is based 
upon a new form of gas-burner which, aided by suitable 
bellows, can be used as a convenient source of heat for most 
operations of the chemical laboratory and lecture table. It 
will boil a quantity of liquid, exceeding two gallons, at once ; 
it will raise a 4| r inch fire-clay crucible to full redness ; it 
will fuse anhydrous caibonate of soda in greater quantity 
than is required for the analysis of a siliceous mineral; and 
it will melt small quantities of sterling silver. This amount 
of power is sufficient for most chemical and many metallur¬ 
gical operations. 

Fig. 47 represents the gas-burner of tins apparatus. The 
gas is supplied by the horizontal tube, whence it passes 
through a set of small holes into the box a, in which it mixes 
with atmospheric air that enters freely by the holes shown 
in the sketch. The gaseous mixture passes up the vertical 
tube b , and is inflamed at the top, where it burns with a 
single tall blue flame, which gives no smoke, very little light, 
but much heat. In this condition the apparatus differs from 
4 Bunsen’s gas-burner ’ only in size, c represents a thin brass 
cap, which fits the air box a, but moves easily round it; cl 
is a flat cast-iron box with many holes round the margin, 
and a few small ones on the top. This box fits loosely on 
the upper part of the tube b , and when it is placed upon 
it and the gas is lighted the flame produced consists of a 
series of radiating jets, forming a horizontal circular flame 
of about seven inches in diameter. Fig. 48 a shows a ring 
of horizontal flames produced; 47 b gives the single vertical 
flame.* The ring of flame is suited to the purposes of 

* Fig. 48 represents a small variety of this gas-burner, in which the head is 
not removable, but the elllux of the mixed gases is regulated by a sliding valve, 
which is represented by b. 

II 


08 


REVERBERATORY GAS FURNACE. 


boiling and evaporation ; the single flame to ignition and 
fusion: The height of the apparatus represented by fig. 47 
is twelve inches ; the bore of the tube b is one inch ; and the 
diameter of the fire-box d is four inches. 

When a large crucible is to be heated to redness, the 
gas-burner is to be used without the rose, and is to be 
arranged with the furnace fittings that are represented in 
perspective by lig. 49, and in section by fig. 50, and the 
lower part of fig. 51, a , 5, c, d. Letter a represents the gas- 
burner ; fig. 49 b is a tall iron stool; c a chimney which 
collects atmospheric air to feed the flame, and lead it up close 
to the vertical tube of a, by which contrivance the air is 
warmed and the tube cooled ; d is a furnace-sole or plate 

of fire-clay ; / is a re¬ 
verberatory dome, the 
interior of which is 
best shown in the sec¬ 
tion fig. 50 ; e is a cast- 
iron ring or trivet, re¬ 
presented more clearly 
in fig. 52 ; g is an iron 
chimney, 24 inches 
^ loner and 34 inches 


Fig. 47. 


Fig. 48. 


h 

d 


iiJIJiy 

Ma 

| ftP" i 


i 

3 


□Z 

1 -1 

'IB 


wide ; and h a damper to lessen the draught when small 
crucibles are to be heated. The height of this apparatus from 
a to the top of/ is 24 inches ; and the external diameter of the 
dome / is about 8 inches. The crucible, which may be from 
4| to 4| inches in height, is placed on the iron ring e fig. 50 
or fig. 52, and that on the clay sole d, and it is then covered 
by the dome /. The gas should be lighted after the crucible 
is placed in its position and before the dome is put on. The 
dome and the chimney are then to be added and the opera¬ 
tion allowed to proceed. With a crucible of the above size, 
the damper h is not required; but it must be used when the 
crucible is under 4 inches in height, otherwise the draught 
occasioned by extra space within the dome causes the flame 
to blow down. The damper must be put on the chimney 
before the chimney is put on the dome. The iron ring (fig. 
52 or e fig. 50) suits crucibles of different sizes, according to 
which side of it is turned uppermost. 


















REVERBERATORY GAS FURNACE. 


99 



The figures show that a crucible mounted in this furnace 
can lose very little heat by radiation or conduction, and 
lienee it is that a small gas flame produces a powerful effect. 
In half an hour a 4^-inch clay crucible, filled and covered, 


Fig. 49. 


Fig. 51. 


Fig. 50. 



can be heated to full redness. The progress of the ignition 
can be easily examined by lifting up the chimney g and the 
dome / by their respective wooden handles. But the action 
of the furnace can also be judged of by a peculiar roaring 






















































































100 


LARGER MELTING GAS FURNACE. 


noise which it produces. If the gas and air are mixed in 
due proportions, the roar is regular and continuous ; if there 
is too much gas the roar is lessened, if too much air the roar 
is increased, but is rendered irregular and intermittent. The 
greater the noise, the greater the heat in the furnace. And 
when the roar becomes spasmodic the flame is on the point 
of blowing down. To prevent that occurrence, the pro¬ 
portion of air must be lessened or that of gas increased. 

The following arrangement is convenient when small 

o o 

crucibles are to be strongly heated : anhydrous carbonate 
of soda in quantities exceeding 1,000 grains can be thus 
readily fused in a platinum crucible, and sterling silver can 
be melted in a clay crucible. It is also available for ignitions 
or fusions in small porcelain crucibles. Fig. 51 represents the 
arrangement of apparatus, as seen in section: a is the gas- 
burner ; b the stool; c the air chimney, and cl the furnace- 
sole, as already explained ; i is a cylinder of fire-clay, 4 inches 
high, and 4J> inches diameter ; k is a fire-clay furnace, in 
which is placed a small cast-iron ring about 2 inches in dia¬ 
meter, similar in form to that represented by fig. 52, and on 
this ring the platinum crucible is adjusted ; l is a fireclay 
or plumbago reverberatory dome; and g is the chimney that 
forms part of the furnace represented by fig 49. The 
crucible being adjusted, the gas lighted, and the dome and 
chimney put on, the lapse of twelve or fifteen minutes, 
according to the quality and pressure of the gas, suffices for 
the fusion of 1,000 grains of carbonate of soda in a platinum 
crucible. At the heat which this furnace produces the cast- 
iron ring does not melt nor alloy with the platinum crucible 
placed upon it. 

By a modification of these arrangements, Mr. Griffin has 
made a gas furnace for melting quantities of lead, zinc, anti¬ 
mony, &c. This is represented by fig. 53. The iron crucible 
will contain nearly 30 lbs. of lead and about 24 lbs. of zinc. 
The burner readily melts these quantities, and then, with a 
diminished quantity of gas, will keep the metals fluid. The 
metals being protected from the air suffer little loss by oxida¬ 
tion. Such operations as the granulation of zinc are per¬ 
formed with this apparatus with great facility; it serves also 


PRINCIPLES OF HEATING BY GAS. 


101 


for baths of fused metal. In a large furnace of this kind, 
made for a special operation, GO lbs. of zinc have been melted 
with ease, and the inventor believes that, used in this manner, 
the burner is powerful enough to melt 
a hundredweight of zinc. FlG - 53 • 

The principles of heating by gas, 
which have led Mr. Griffin to the con- c=a dL-. 
struction of these gas furnaces, may be 
summed up as follows : When a crucible 
or other solid body is to be heated, it is 
to be wrapped in a single flame at the 
point of maximum heat, and loss of heat 
by radiation and conduction is to be 
prevented by the interposition of non¬ 
conducting materials (plumbago or fire¬ 
clay) ; and when liquids are to be boiled 
or evaporated, particularly when they 
are contained in vessels of glass or 
porcelain, the flame is to be broken up 
into numerous horizontal jets, and these 
are to be made to supply a large and 
regular current of highly-heated air, 
by which alone, and not by the direct application of the 
flame, the vessel that contains the liquid is to be heated. In 
both cases provision must be made to secure a sufficient 
draught of air through the furnace, because every cubic foot 
of gas requires for combustion 10 or 12 cubic feet of air, 
and the gases which have done their duty must be rapidly 
carried away from the focus of heat. If the steam, the car¬ 
bonic acid gas, and the free nitrogen which constitute the 
used-up gases are not promptly expelled, fresh gaseous 
mixture in the act of producing additional heat by com¬ 
bustion cannot get near the object that is to be heated, 
and the heat so produced out of place is wasted. 

Bunsen’s gas-burner, whatever its size, is subject to two 
defects: sometimes the flame burns white and smoky, and 
sometimes it blows down, the gaseous mixture explodes, and 
the gas then burns with a smoky flame in the tube. The 
remedies for these defects are as follows : If the flame is 































102 


BUNSEN \S GAS-BURNER. 


white only when the gas is turned on very full, the remedy 
is to lessen the supply of gas; but if the ilame continues to 
burn white at the top when the gas is gradually turned off and 
the mass of ilame slowly sinks, then the holes which deliver 
the gas from the supply pipe into the air-box a (fig. 47) are too 
large, and are placed too directly under the centre of the 
vertical tube b (fig 47), and these defects must be corrected 
in the instrument. Finally, when the flame blows down it is 
because the supply of atmospheric air is too large in propor¬ 
tion to the supply of gas, and their relative proportions must 
be altered. To effect this alteration the cap c is to be turned 
round on the air-box a so as partially to close the holes, and 
thus lessen the supply of air. If, when the gas is alight the 
flame needs to be lowered, first the supply of air is to be 
lessened and then the supply of gas. If the flame is to be 
enlarged, first the supply of gas must be increased and then 
the supply of air. In short, to prevent the flame blowing 
down, the gas must always be placed in excess, and then 
have the proper quantity of air adjusted to suit it by means 
of the regulator c. When gas-burners of this description 
have to be used in a locality where the pressure of the gas 
is slight, especially in the daytime, there is a constant ten¬ 
dency in the flame to blowdown. The best way to prevent 
that occurrence is to supply the gas by a pretty wide tube-, 
and to see that the current of gas is not checked by a very 
narrow bore in the plug of an intervening stop-cock, which 
is often the unsuspected cause of want of pressure in the 
supply of gas. If this does not suffice to prevent the 
blowing down of the gas, the holes which admit the gas 
from the supply pipe into the box a of the burner should be 
enlarged, more or less according to necessity. A large supply 
of gas compensate#, to some extent, for want of pressure. 

When a steady and long-continued heat is desired from a 
Bunsen’s burner it is proper to use two stop-cocks and a 
length of caoutchouc tube between them. One of these 
stop-cocks is to be affixed to the burner, and the other to 
the supply pipe. The latter is to be opened wider than is 
necessary to supply the required quantity of gas, and the 
former is to be used to regulate the supply to the burner 


METHOD OF MOUNTING CRUCIBLES. 


103 


exactly ; under these circumstances, if another stop-cock is 
opened and gas burnt in the immediate neighbourhood, the 
flame does not so readily blow down in the regulated burner 
as it does when only the stop-cock on the supply pipe is 
used. 

When a crucible is suspended by wires or by a ring over 
the flame of a spirit lamp or gas-burner, the flame and the 
hot air supplied by the flame strike the crucible for an 
instant and then pass away to do no more good. At the 
same time the effect of the heating power on the crucible is 
lessened by other circumstances ; namely, by radiation on all 
sides, by a mass of cold air which constantly rises around and 
in contact with it, and by the conducting power of the 
metallic apparatus which supports both the crucible and the 
lamp. These losses are avoided if the crucible is enclosed 
in a furnace made of a non-conducting material, such as fire¬ 
clay, which can absorb and retain heat. In the descriptions 
of the gas furnaces, and in that of Charles Griffin’s oil-lamp 
furnace, several methods of mounting crucibles in fire-clay 
jackets have been shown ; and we will now describe some of 
Mr. Griffin’s fittings that may be used to construct temporary 
table furnaces for crucibles that arc to be exposed to the 
flame produced by gas, oils, or spirit, up to a temperature 
close upon, but not quite up to, a white heat; that is to say, 
up to a heat that will readily melt anhydrous carbonate of 
soda and small quantities of silver, and so be fit for many 
metallurgical operations, but which will not melt copper nor 
cast-iron. 

Fig. 54 represents sections of cylinders of fire-clay which 
are drawn on a scale of 1 to 8, and have the relative heights 
and bores represented in the figures. The clay pieces, that 
is to say, as many of them as are necessary for a given pur¬ 
pose, can be adjusted over a gas-flame by means of a tripod 
(fig. 49) or a clay support. 

The crucible to be operated upon is to be supported on a 
toothed ring made either of cast iron or fire-clay, such as are 
represented by figs. 52 and 55. Fig. 52 is a ring of cast 
iron, h representing it in section and i as seen from above. It 
is about two inches in diameter, and has three teeth project- 


104 


MOUNTS FOR CRUCIBLES. 


ing towards tlie middle of tlie ring. This ling can be sup¬ 
ported by any of the clay cylinders whose bore does not 
exceed two inches. Fig. 55 is a ring of fire-clay of 4 inches 
external diameter, and 1 inch in thickness, provided with 
three teeth that project inwards and upon which a crucible 
can be supported without injuring the draft of the gas furnace. 

Both these grates will support crucibles at tlie highest tem¬ 
perature which can be produced by spirit, oil, or gas, without 
a blast of air ; but at a white heat produced by any of these 
fuels with a blast of air, the iron ring melts, and if the heat 
is long continued, those of fire-clay soften and partially give 
way. When the fire-clay grate (fig. 55) is required to sustain 
a very high temperature for a considerable time, it is proper 
to have it made of G inches diameter, as represented by fig. 
54 p , the air-way in which is the same as that of the small 
grate, but the clay ring is much stronger. 

The grate is fixed above the ilame at a distance which is 
found by trial to place the crucible on the point of greatest 
heat. Commonly a 4-inch cylinder (54 h or 54 g) placed 
upon a suitable support serves the purpose. The bore of 
the cylinders at the bottom must be wider than the burner, 
to allow of a considerable influx of atmospheric air around 
the flame. The grate is placed on this cylinder, the crucible 
on the grate, and then another cylinder around the crucible. 
The choice of this upper cylinder depends entirely upon the 
size of the crucible that is to be heated. Whatever tlie size 
of the crucible, the cylinder must be so chosen as to fit the 
crucible as accurately as possible, leaving between it and the 
furnace walls an open space of not less than -J- inch, nor more 
than \ inch all round. If the upper cylinder is not con¬ 
tracted at top like 54 e f g, then a cylinder of narrow bore, 
such as 54 a or c, must be put upon it, in order to deflect the 
flame, and the rising current of hot air upon the top of the 
crucible, and thus produce a reverberatory furnace. Finally, 
an iron chimney, 2 or 3 feet long, must be put upon the 
furnace, to force up a draft of air sufficient to feed the flame. 

Suppose a small rose gas-burner is to be arranged for an 
ignition, with the use of a fire-clay support, the combination 
of pieces necessary for the purpose may be those represented 


105 


MOUNTS FOR CRUCIBLES. 


by fig. 50, where a is the fire-clay support, and the rest 
of the pieces are those which are shown at fie;. 54, and 


described at the letters 
placed against each of them 
in this figure. It is evident 
that the application of this 
furnace to crucibles of dif¬ 
ferent sizes depends upon 
the proper choice of the 
cylinders here marked i and 
e. Of course there is only 
a limited choice of crucibles 
suitable for such operations. 
Th ree inches is the extreme 
width between the furnace 
walls of any of the pieces 
in fig. 54, from a to g, and 
though larger cylinders coidd 
be used, such as i to o, it must 
be remembered that the 
flame of a lamp without 
blast has only a limited 
power, and that although a 
given flame will fuse 1,000 
grains of carbonate of soda 


Fig. 54. 



in a platinum crucible, it 
may only heat to a moderate j 
redness a large clay cru¬ 
cible. Yet, considering that 
low degrees of heat are suitable for many purposes, it is con¬ 
venient to have the power of readily adjusting a tem¬ 
porary furnace to the bulk of any crucible 
which it is desired to heat. 

The clay pieces (fig. 54 i to p) are thos 
that have been expressly designed for the blast 
oil furnace already described ; but these can 
also be used for spirit and gas furnaces, the 
respective sizes being chosen in each case 
according to the size of the crucible that is to be ignited. 






































































































































































































































































IOC) 


TEMPORARY GAS FURNACES. 


Fig. 56. 


Iii respect to the means of supporting a crucible, it lias been 
shown that clay trivets with a wide flange, namely, the 6-inch 
trivets fig. 54 p, will support a crucible containing 5 lbs. of 
iron until that quantity of iron is melted, even under the 

operations of a blast: so that it is evident 
that this method of supporting a crucible in 
a gas flame may be always depended upon 
when no blowing-machine is employed. 
The discovery of the fact that a trivet of 
fire-clay of the form of fig. 55 could sustain 
a crucible bearing 5 lbs. of cast iron, until 
that quantity of iron has melted under the 
action of a blast, induced Mr. Griffin to 
make some experiments on the joint use of 
a small blast gas-burner and the small fire¬ 
clay cylinders that are here described, and 
these experiments led to the construction 
of the Miniature Blast Gas Furnace al¬ 
ready described, an apparatus that justifies 
the recommendation that has been given 
of the use of these cylinders ; for in the 
miniature blast gas furnace, the chemist 
has an instrument which possesses great 
power in a small compass, and convenient 
form, the cost of which is a trifle, and which by the addition 
or exchange of a few fire-clay cylinders can be modified 
to suit a great variety of operations at high temperatures. 

Fig. 57 . Tig. 57 represents the 

gas-furnace arranged for 
boiling the evaporation : a 
is the gas-burner; b an iron 
stool with three legs ; c a 
furnace body or iron jacket 
lined with plumbago or 
fireclay. This furnace may 
be 14 inches high and 9 
inches in diameter. The 
three brackets fixed on the 
upper part of the jacket serve to support the vessel that 













































































































LUTES AND CEMENTS. 


107 


contains the liquid that is to be boiled or evaporated. A 
porcelain basin of 1G or 18 inches in diameter can be thus 
supported. It is important to allow between the jacket c 
and the evaporating basin plenty of space for the escape 
of the heated air, which ascends from the interior of the 
furnace. When the evaporating basin is of small dia¬ 
meter, it may be supported on iron triangles, placed in 
the furnace c. The section shows that around the vertical 
tube of the gas-burner a there is in the bottom of the fur¬ 
nace c a circular opening which is of 2 inches diameter, and 
through which air passes freely, partly to feed the flame and 
partly to be heated by the flame and be directed upwards 
in a continuous current upon the lower surface of the " 
basin that is to be heated. The flame within the furnace 
burns steadily. No side currents of air agitate it. No part 
of it touches the basin, which should receive its heat solely 
from the mass of ascending hot air. The gas-burner thus 
arranged and supplied by a gas pipe of ^-inch bore, burns 
about 3 cubic feet of gas in an hour, and the flame which 
it produces, acting upon water contained in an open por¬ 
celain evaporating basin, will heat from 60° to 212° F.— 

1 quart in 5 minutes 

1 gallon in 15 „ 

2 gallons in 30 „ 

and when the water boils it is driven off in steam at the 
rate of more than a gallon of water per hour. The method 
is consequently applicable to distillation on a small scale, 
and to numerous other laboratory operations. 

Lutes and Cements.— It may be as well to mention in this 
part of the work the various lutes and cements which may 
be employed, either in fire operations or in making good 
joints in experiments with gases or liquids. The following 
are the principal kinds : The best fire lute is that described 
by Mr. Parker, and is composed of good clay two parts, sharp 
washed sand eight parts, horse-dung one part. These 
materials are to be intimately mixed ; and afterwards the 
whole is to be thoroughly tempered like mortar. Mr. Watt’s 
fire lute is an excellent one, but is more expensive. It is 
made of finely-powdered Cornish (porcelain) clay mixed to 


JOS 


LUTES AND CEMENTS. 


the consistence of thick paint with a solution of borax in the 
proportion of 2 ounces of borax to a pint of hot water. 

Fat Lute is prepared by mixing line clay, in a fine 
powder, with drying oil, so that the mixture may form a 
ductile paste. When this paste is used the part to which it is 
applied ought to be very clean and dry, otherwise it will 
not adhere. Glazier’s putty is very similar to this. 

Koman Cement. —This must be kept in well-closed ves¬ 
sels, and not moistened until the instant it is required for use. 

Plaster of Paris. —This is mixed with water, milk, or 
weak glue, or starch water. 

These three lutes stand a dull red heat: the two latter 
* may be rendered perfectly impermeable to gaseous bodies 
by being smeared over with oil, or a mixture of oil and wax. 

Linseed or Almond Meal, mixed to the consistence of a 
paste with water, milk, lime-water, or starch paste. This 
lute is very manageable and impermeable, but does not 
withstand a heat greater than about 500° F. 

Lime and Egg Lute.— If just the sufficient quantity of 
water be added to quick lime to reduce it to a dry powder 
and that is mixed well and rapidly with white of egg diluted 
with its own volume of water, and the mixture spread 
immediately on strips of linen and applied to the part, then 
powered with quick lime, it forms a good cement. Instead 
of white of egg, lime and cheese may be used, or lime with 
weak glue water. This lute dries very rapidly, becoming 
very hard and adhering strongly to glass ; but its great 
inconvenience is the want of flexibility. 

White Lead mixed with Oil. —If this mixture be spread 
upon strips of linen, or bundles of tow, it acts much in the 
same manner as the lime lutes. 

Yellow Wax is often used as a lute, but it becomes very 
brittle at a low temperature. It may be rendered less brittle, 
and at the same time more fusible, by an admixture of one- 
eighth crude turpentine. 

Soft Cement is prepared by fusing yellow wax with half 
its weight of crude turpentine and a little Venetian red in 
order to colour it. It is very flexible, and takes any desired 
form under the pressure of the fingers. 


LUTES AND CEMENTS. 


109 


Waterproof Cement. —Mr. Edmund Davy, F.B.S., has de¬ 
scribed a cement made by melting in a saucepan, two parts by 
weight of common pitch, and adding to it one part by weight 
of gutta percha, stirring and mixing them well together 
until they were completely incorporated with or united with 
each other. The mixture then formed a homogeneous 
fluid which may be used in this state for many purposes, 
and is remarkable on account of the facility and tenacity 
with which it adheres to metals, stones, glass. It may be 
poured into a large basin of cold water, in a thinner or 
thicker stream, or as a cake. In this state, while warm, it 
is quite soft, but may be soon taken up out of the water and 
drawn out into longer or pressed into shorter pieces, or 
cut or twisted into fragments, which may again be readily 
reunited by pressure. When the cement is cold, or before, 
it may be removed from the w r ater and wiped dry, when it 
is fit for use. It is of a black colour ; when cold, it is 
hard. It is not brittle, but has some degree of elasticity, 
which is increased by a slight increase of heat. It appears 
to be not so tough as gutta percha but more elastic. Its 
tenacity is very considerable, but inferior to gutta percha. 
It softens when put into water at about 100° F. ; and 
if the heat is gradually increased it passes through inter¬ 
mediate states of softness, becomes viscous like bird-lime, 
and may be extended into threads of indefinite length : it 
remains in this state even when exposed for some time in a 
crucible, to the heat of boiling water, at 212° F. ; when 
heated to above 100° F. it becomes a thin fluid. Water 
appears to have no other action upon it but that of softening 
it when warm or hot, and slowly hardening it when cold. 
The cement adheres strongly, if pressed on metal or other 
surfaces, though water be present, provided such surfaces be 
warm. This cement is applicable to many useful purposes. 
It adheres with great tenacity to metals, wood, stones, glass, 
porcelain, ivory, leather, parchment, paper, hair, feathers, 
silk, woollen, cotton, linen fabrics, &c. It is well adapted 
for glazin y windows, or as a cement for aquariums. This 
cement does not appear to affect water, and it will 
apparently be found applicable for coating metal tanks ; 


no 


LUTES AND CEMENTS. 


to secure tlie joints of stone tanks ; to make a glue for 
joining wood, which will not be affected by damp ; and to 
prevent the depredations of insects on wood. 

Resinous, or Hard Cement, is made by fusing together at 
the lowest possible temperature one part of yellow wax and 
five or six of resin, and then adding gradually one part of red 
ochre or finely-powered brickdust (plaster of Paris succeeds 
very well), and then raising the temperature to 212° at least 
until no more froth arises, or agitation takes places, and 
stirring it continually until cold. This cement is employed 
in a hot state. This lute is much used for fixing brass caps, 
&c., to air jars. 

Paper, covered with common glue, is occasionally 
employed. 

Bladders, cut in small strips, are occasionally used in 
covering other lutes, when the pressure of gas is considerable 
or when the lute is subject to strain from any other cause. 
They are digested in water until they become soft and 
flaccid; they are then applied to the part like a piece of 
pasted paper, by the pressure of the hand. These strips 
adhere very strongly to glass or earthenware, and their 
adhesive power may be much augmented by smearing them 
with white of egg. Lastly the joints made in this manner may 
be made firmer by binding them with string or fine wire. 

Caoutchouc.— Tubes of vulcanised caoutchouc form a very 
ready means of attaching one piece of apparatus to another, 
and they possess the peculiar advantage of flexibility, which 
allows the various parts of the apparatus which they cannot 
connect to move in different directions to a slight extent, so 
that the whole is not so likely to be fractured as when con¬ 
nected in an inflexible manner. Caoutchouc is also less 
acted upon by gases and vapours than almost any other 
substance we know; even chlorine attacks it but slowly, 
and when unvulcanised it possesses the valuable property of 
forming a perfect joint when freshly-cut edges are brought 
and pressed together, hence the facility with which it is 
manufactured into tubes. The mode of manufacturing small 
connecting tubes, which are often required to be of unvul¬ 
canised caoutchouc, is as follows: Take a piece of the 



LUTES AND CEMENTS. 


Ill 


sheet caoutchouc of the required size, and warm it either 
in the hand or before a lire, until it is perfectly soft; then 
place it around a glass rod of the requisite size, pressing the 
edges close together with the fingers; when close together 
cut oil the superabundance with a sharp pair of scissors, 
and the newly-cut edges will unite by simple pressure of the 
nail. When well executed the joint is scarcely apparent. 
In order to prevent tire caoutchouc from adhering to the 
rods on which the tube is formed, a little moisture or dry 
starch may be employed. When caoutchouc is not at hand, 
oiled paper may be substituted, the joint being made of 
wax. 


Faraday gives the following directions for luting iron, 
glass, or earthenware retorts, tubes, &c. for furnace operations. 
When the lute has to withstand a very high temperature it 
should be made of the best Stourbridge clay, which is to be 
made into a paste varying in thickness according to the 
opinion of the operator. The paste should be beaten until 
it is perfectly ductile and uniform, and a portion should then 
be flattened out into a cake of the required thickness, and 
of such a size as shall be most manageable with the vessel 
to be coated. If the vessel be a retort or flask, it should be 
placed in the middle of the cake, and the edges of the latter 
raised on all sides and gradually moulded and applied to 
the glass ; if it be a tube if should be laid on one edge of 
the plate, and then applied by rolling the tube forward. In 
all cases the surface to be coated should be rubbed over 
with a piece of the lute dipped in water for the purpose of 
slightly moistening and leaving a little of the earth upon it; 
if any part of the surface becomes dry before the lute is 
applied it should be remoistened. The lute should be 
pressed and rubbed down upon the glass successively from 
the part where the contact was first made to the edges, for 
which purpose it is better to make them thin by pressure 
and also somewhat irregular in form, and if at all dry they 
should be moistened with a little soft lute. The general 


thickness may be about ^ to ^ of an inch. 

Being thus luted, the vessels are afterwards to be placed 
in a warm situation, over the sand-bath or near the ash-pit, 


112 


LUTES AND CEMENTS. 


or in the sun’s rays. They should not be allowed to dry 
rapidly or irregularly, and should be moved now and then 
to change their positions. To prevent cracking during 
desiccation, and the consequent separation of the coat from 
the vessel, some chemists recommend the introduction of 
fibrous substances into the lute, so as mechanically to increase 
the tenacity of its parts. Horse-dung, chopped hay and 
straw, horse and cow-hair, and tow cut short, are amongst 
the number. When these are used, they should be added in 
small quantity, and it is generally necessary to add more 
water than with simple lute, and employ more labour to 
ensure a uniform mixture. It is best to mix the chopped 
material with the clay before the water is put to it, and by 
adding the latter, to mix at first by stirring up the mass 
lightly with a pointed stick or fork ; it will then be found 
easy, by a little management, to obtain a good mixture 
without making it very moist. 

The luting ought to be made as dry as possible consis¬ 
tent with facility in working it. The wetter it is the more 
liable to crack in drying, and vice versa. 

%j O 7 

Mr. Willis recommends, when earthenware retorts, &c., 
are to be rendered impervious to air, the following coating : 
One ounce of borax is to be dissolved in half a pint of boil¬ 
ing water, and as much slaked lime added as will make 
a thin paste. This composition is to be spread over the 
vessel with a brush, and when dry, a coating of slaked lime 
and linseed oil is to be applied. This will dry sufficiently 
in a day or two, and is then fit for use. 

Iron Cement.— This mixture is used for making perma¬ 
nent joints generally between surfaces of iron. Clean iron 
borings or turnings are to be slightly pounded, so as to be 
broken but not pulverised : the result is to be sifted 
coarsely, mixed with powdered sal-ammoniac and sulphur, 
and enough water to moisten the whole slightly. The pro¬ 
portions are 1 sulphur, 2 sal-ammoniac, and 80 iron. No 
more should be mixed than can be used at one time. Mr. 
Cooley states that he is informed by one of the first engineers 
in London that the strongest cement is made without sulphur, 
and with only one or two parts of sal-ammoniac to 100 of iron 



CRUCIBLES, CUPELS, ETC. 


113 


borings: but that when the work is required to dry rapidly, 
as for the steam joints of machinery wanted in haste, the 
quantity of sal-ammoniac is increased a little, and a very 
small quantity of sulphur is added. This addition makes it 
set quicker, but reduces its strength. Several excellent 
cements are described in Cooley’s ‘ Cyclopaedia of Practical 
Receipts.’ From these the following are selected :— 

Beale’s Cement. —Chalk 60 parts : lime and salt, of each 
20 parts ; Barnsey sand 10 parts ; iron filings or dust and 
blue or red clay of each, 5 parts. Grind together and cal¬ 
cine. This is patented as a fire-proof cement. 

Boiler Cement. —Dried clay in powder 6 lbs., iron filings 
1 lb., made into a paste with boiled linseed oil. This is 
used to stop leaks and cracks in iron boilers, stoves, &c. 

Bruyere’s Cement.— Clay 3 parts ; slaked lime 1 part: 
mix and expose them to a full red heat for 3 hours, then 
grind to powder. 

This makes a good hydraulic cement. 

Oxychloride of Zinc Cement. —In solution of chloride of 
zinc of 1*49 to 1*65 specific gravity, dissolve 3 per cent, of 
borax or sal-ammoniac, and then add oxide of zinc which 
has been heated to redness, until the mass is of a proper 
consistence. This cement becomes as hard as marble. It 
may be cast in moulds like plaster of Paris. 

Crucibles, Cupels, etc. —The crucibles best known in 
commerce are the Hessian, the Cornish, the Stourbridge, and 
the London clay crucibles ; charcoal, plumbago, iron, por¬ 
celain, platinum, silver and gold crucibles are also required 
in small operations. Of the clay crucibles, the London pots 
are much to be preferred on account of their very refractory 
nature. They resist the action of fused oxide of lead better 
than most clay crucibles, and they are also much better 
made than the two other kinds, being much smoother and 
more regularly formed. They have the form of a triangular 
pyramid (see fig. 58, crucibles and cover), and are made in 
such sizes that they fit one into the other, forming nests. The 
triangular form is very convenient, because there are three 
spouts, from either of which can be poured the fused con¬ 
tents of the pot. The Cornish crucibles are circular, and do 

i 


114 


PLUMBAGO AND CLAY CRUCIBLES. 


not stand changes of temperature so well as the London 
pots, neither can they endure such an extreme ol heat, 
Fm. 58. for they agglutinate and run to¬ 

gether at a temperature which 
does not touch the others. 
Dr. Percy says they are more 
generally useful than any other 
crucible. The Hessian pots are 
the worst of all; they do not 
stand moderate change of tem¬ 
perature without risk of frac¬ 
ture, so that they require to be 
very carefully used. There is 
also another kind of pot in 
use, made of the same material as the London crucibles, 
termed a c skittle pot,’ from its resemblance to the or¬ 
dinary wooden skittle or ninepin. They are exceedingly 
useful for the fusion of large masses of matter, or such 
substances as boil or bubble much when heated. Plumbago 
or graphite crucibles are rapidly superseding all other kinds 
when metals have to be melted. They possess many advan¬ 
tages over clay crucibles. Their surface is very smooth ; 
they are not liable to crack, however violent the changes of 
temperature may be to which they are subjected ; they 
bear the highest heat without softening, and can be used 
repeatedly. Owing to the reducing property of the carbon 
they contain, they must not be employed when oxidising 
actions are required. 

The Patent Plumbago Crucible Company have recently 
introduced a very excellent fluxing crucible. It is made 
of fine white china clay, is perfectly smooth inside and 
out, and will stand very high temperatures without softening. 

Stourbridge clay crucibles are not much used. They 
require the greatest care in using them, and are spoilt after 
the first operation. 

Porcelain crucibles are not used in large assaying or 
metallurgical operations, but they are invaluable in small 
laboratory experiments. They arc practically infusible, 
are little liable to crack, and are almost unacted on by 




PLUMBAGO AND CLAY CRUCIBLES. 


115 


reagents and fluxes. In many cases they will replace the 
more expensive platinum crucibles, and where easily re¬ 
ducible metals are under treatment, they must be used in 
preference to platinum. 

Crucibles in order to be perfect and capable of being 
used indifferently for any operation, ought to possess the 
four following qualities: firstly, not to break or split when 
exposed to sudden changes of temperature ; secondly, to be 
infusible ; thirdly, to be only slightly attacked by the fused 
substances they may contain ; fourthly and lastly, to be 
impermeable, or nearly so, to liquids and gases. But as it 
is very difficult to unite all these qualifications, various kinds 
of pots are made to fulfil one or more of them. 

In order to render crucibles capable of withstanding 
changes of temperature without breaking, a certain proportion 
of substances infusible by themselves, is mixed with the 
pasty clay; sand, Hint, fragments of old crucibles, black-lead, 
and coke, are used for this purpose. They are reduced to 
a state of division more or less fine, according to the grain 
of the clay paste. For ordinary pots, the powder ought not 
to be very fine; but for porcelain crucibles it ought to be as 
fine as flour. The choice of these various bodies depends 
upon the use for which the crucible is intended. 

The most refractory crucibles are those made with the 
pure clays, or such as contain little or no oxide of iron, and 
especially free from calcareous matters. Amongst those clays, 
the best are those which contain most silica; nevertheless, 
these are not absolutely infusible, and in the high tempera¬ 
ture of a wind furnace they sometimes soften so much as 
actually to fall into a shapeless mass. This defect, as before 
stated, can be in some measure diminished by mixing with 
the clay a quantity of graphite or coke ; either of these 
substances forms a kind of solid skeleton, which retains the 
softened clay, and prevents its falling out of shape. 

Coke and black-lead are more efficacious than sand, 
because they have no action on clay, whilst sand forms a 
fusible compound with it. If too large a quantity of black- 
lead or coke be employed, it gradually consumes in the fire, 
and the pots become porous, and break at the least move • 


116 


PLUMBAGO AND CLAY CRUCIBLES. 


ment. Wood charcoal can be used instead of black-lead 
or coke, but is not so good, as it burns more readily. 

Black-lead crucibles are generally composed of 1 part of 
refractory clay, and from 2 to 3 of black-lead. These pots 
withstand all possible changes of temperature without 
cracking, and their form is rarely changed by the heat, not 
because they are absolutely infusible, but because they are 
supported by the skeleton of graphite. 

Crucibles into whose composition carbonaceous matters 
enter, reduce any oxides that may be heated in them, and 
hence are inconvenient in certain cases. They can, never¬ 
theless, be employed in all cases by giving them a lining of 
clay, which must be tolerably thick, and well dried before 
use. 

Earthen crucibles, which have not been baked at a white 
heat, are more or less permeable to liquids and gases, 
according to the grain. In order to render them imperme¬ 
able to liquids, they must be heated to such a temperature as 
will suffice to fuse the outside. When treated in this way, 
however, they are very liable to crack with sudden changes 
of temperature: the best method, therefore, of rendering 
them capable of containing water, &c., is to coat them with 
the mixture of borax and lime described as Willis’s lute. 

In order that crucibles may resist the corrosive action of 
the fused substances contained within them, they must be 
as compact as possible, and the substance of which they are 
made must have little or no tendency to.combine with the 
fused contents. The metals and their non-oxidised com¬ 
pounds neither attack clay nor black-lead; but there are, 
nevertheless, some metallic substances, galena, for instance, 
which, without exercising any chemical action on earthy 
matters, have the property of filtering through their pores. 

The readily reducible oxides gradually corrode black-lead 
crucibles and those pots in the composition of which coke 
enters, by burning the carbonaceous matter. The greater 
number of these oxides, the alkalies, earths, and glasses 
(which are fusible silicates, borates, &c.), act more or less 
powerfully on the earthy base of all crucibles ; so that these 
substances are most difficult to keep in fusion for any 


GOOD AND BAD CRUCIBLES. 


117 


length of time. They attack the crucible layer by layer, 
dissolving the substance of which it is composed, and after a 
lapse of time rendering it so thin that it cannot withstand 
the pressure of the molten mass within it; and the fracture 
of the pot, and consequent loss of contents, is inevitable. 

Under the same circumstances, all those crucibles whose 
texture is loose, are more readily corroded than those with a 
firm, compact body; because the corrosive substance filters 
to a certain depth in the former crucibles, and, in con¬ 
sequence, has a larger surface to act upon than when it is 
contained in a compact pot. 

Earthen crucibles may be assayed by noticing the time 
they will contain fused litharge, which exercises a very 
corrosive action on them, honey-combing them in all direc¬ 
tions ; and those pots which contain it longest without 
undergoing much damage, may be considered the best. 
However, this method of assay is not exact, even by taking 
into account the thickness of the pot, for litharge runs through 
crucibles; firstly, because it is very fusible, and easily filters 
through their pores; and secondly, it has the property of 
forming fusible compounds with all the silicates by com¬ 
bining with them. From these remarks, it will be evident 
that a crucible whose grain is loose will readily allow litharge 
to pass through it, however slightly its substance may be 
fusible or acted on; or, on the contrary, it may be very 
easily acted on (even when infusible) when it has an ex¬ 
tremely fine grain ; so that the promptitude with which a 
crucible is traversed by litharge bears no relation to its fusi¬ 
bility. A crucible of pure quartz will be very readily attacked 
by litharge, because the latter has much affinity for silica, 
and the simple silicates of lead are all very fusible ; whilst a 
crucible composed of silica, alumina, and lime, which by itself 
is very fusible, would be corroded less rapidly, because the 
oxide of lead has much less affinity for the earths than it 
lias for the silica ; moreover, it forms less fusible compounds 
with the earths than with silica alone. The assays of cru¬ 
cibles with litharge, if not of use in ascertaining their degree 
of fusibility, fulfils perfectly its object when it is wished to 
prove the resistance a crucible has to the corrosive action of 


118 


CHARCOAL CRUCIBLES. 


various bodies in a state of fusion ; for of all fusible sub¬ 
stances, none exercise such a powerful action on earthy 
matters as litharge. 

Crucibles ought not only to resist the corrosive action of 
those bodies they may contain, but also that of the ash pro¬ 
duced by the combustion of the fuel in which they may be 
placed. These ashes being often calcareous, alkaline, or 
ferruginous, act on the clayey part of the crucibles exactly 
as the fluxes. Whence it follows, that those crucibles which 
contain litharge longest, will also resist the action of the 
fluxes best. 

In order to ascertain the fusibility of a crucible, a direct 
experiment must be made, either by heating a piece in a 
crucible lined with charcoal, and scertaining if its angles be 
rounded, if its substance has become translucid, &c. ; or, 
better still, by heating the crucible to be assayed with another 
whose properties are well known. 

As to permeability, it may approximately be ascertained 
by filling two crucibles with water, and noting what length 
of time is required to empty them completely ; the crucible 
which contains it longest being, of course, the least per¬ 
meable. 

To prove if a crucible be able to sustain great changes of 
temperature without breaking, introduce it, perfectly cold, 
into a furnace full of lighted coal: take it out when reddish 
white, and expose it to a current of cold air produced by a 
bellows or otherwise : if it stand these trials, it may be 
heated afresh and plunged red-hot into water, and if it be 
not broken, placed immediately in the fire. The best pots 
support all these operations without breaking ; but it often 
happens that they are filled with innumerable small fissures, 
through which fused matters can pass. This can be ascer¬ 
tained by fusing rapidly in the assay pot a quantity of 
litharge: if these be present, the fused oxide will readily 
filter through them. 

Charcoal Crucibles. —As all oxidised matters act readily 
on clay pots, and a great number of the metals and their 
compounds adhere to them, they have long since been 
replaced, under certain circumstances, by charcoal crucibles, 


CHARCOAL CRUCIBLES. 


119 


which do not possess these disadvantages. The older assayers 
used merely a piece of charcoal, with a hole made in it, and 
then bound round with iron orother wire. The use of these 
has, however been abandoned for some time, and earthen¬ 
ware crucibles lined with charcoal have been substituted 


Fio. 59. 



a b c 


(see fig. 59, a , b , and c). These may be considered as char¬ 
coal pots enveloped with refractory clay ; they are solid, 
always free from cracks, and easy of preparation, and they 
have the same properties as the solid charcoal crucibles 
without their inconveniences. 

In order to prepare these crucibles, the charcoal must be 
chosen carefully, so as to contain no foreign substances; it 
must be pulverised and passed through a sieve ; the powder 
moistened with water, mixed with a spatula, and then 
kneaded with the fingers until it just adheres, and forms 
adhesive lumps without being sufficiently wet to adhere to 
the hand. Some advise the addition of gum to the water 
with which the charcoal is moistened. The crucible is 
moistened slightly by being plunged into water, and with¬ 
drawn as speedily as possible, and about half an inch in 
depth of the charcoal paste, prepared as above, placed in it; 
the paste is then pressed firmly down, by means of a wooden 
pestle : the blows are to be slight at first, and then increase 
in force until it is as firm as possible : another layer is then 
applied and pressed as before, and the process repeated 
until the crucible is quite full, taking great care to render nil 



LINED CRUCIBLES. 


1‘20 

as firm as possible, especially at the sides. In order to make 
each layer adhere firmly to the other, the surface must be 
scratched rather deeply with the point of a knife before a 
new layer is applied. When the crucible is completely filled, 
a hole is to be scooped in the charcoal of about the form of 
the pot. The sides are then rendered smooth by friction 
with a glass rod. This is absolutely necessary, so that the 
metallic globules produced in an assay may not be retained 
by the asperities of the lining, but may be readily enabled to 
unite into one button. When a lined charcoal pot is well 
made, its sides are very smooth and shining. For ordinary 
use, the lining may be f ths of an inch thick at the bottom 
and -gth or so at the sides ; but in some cases, for instance, 
when the substance to be fused is capable of filtering 
through the lining and attacking the pot as a flux, it must 
be at least twice the above thickness in every part. 

Lined crucibles have many advantages over plain crucibles. 
The lining gives them greater solidity, and prevents a loss of 
shape when softened ; for plain crucibles are always three- 
fourths empty when their contents are fused, on account of 
contraction in volume: the pots then have nothing to sus¬ 
tain their sides when they soften towards the end of the 
assay, at which period the highest temperature is employed. 
Besides, vitreous matters do not penetrate the lining, and, 
exercising no action on it, can be obtained in a state of 
purity, and the exact weight determined : if fused in a plain 
pot, the weight could not be ascertained, because a portion 
would adhere to the sides, and the resulting mass would not 
be pure, having taken up a portion of the crucible in which 
the fusion was effected. 

The lining, too, effects the reduction of certain metallic 
oxides by cementation, and does away with the necessity of 
adding powdered charcoal to the body to be reduced. This 
property is very valuable, because, when an oxide is reduced 
by mixing it with charcoal, an excess must always be em¬ 
ployed, and this excess remains with the metal, and prevents 
its exact weight from being ascertained. No oxidising sub¬ 
stances or bodies which readily part with oxygen (oxide of 
copper, for example) must be calcined in a plumbago or 


LIME CRUCIBLES. 


121 


charcoal lined crucible, unless indeed the chemical union of 
the charcoal with the oxygen is desired. 

Lime Crucibles.— Some years ago Deville proposed the 
use of crucibles cut out of solid blocks of pure lime, in order 
to prevent the introduction of carbon and silicon into metals 
and alloys during the process of fusion. 

The results of experiments made with such crucibles were 
found to be extremely satisfactory, and metals fused therein, 
as iron, manganese, nickel, cobalt, &c., were obtained far 
purer and more malleable and ductile than when fused in 
the usual clay or brasque crucibles. Unless, however, the 
crucibles required were of very small size, it was found diffi¬ 
cult to obtain blocks of lime for shaping them sufficiently 
large and free from flaws ; and experiment showed a con¬ 
siderable loss, both by breakage when shaping them, and 
by their cracking when in the furnace. In order to 
obviate this, trials were made with clay crucibles lined with 
lime, but ineffectually, as these crucibles invariably melted 
down before the requisite heat was arrived at—a result due 
to the action of the lime itself upon the clay outer crucible. 

Mr. David Forbes, F.R.S.,has published in the 4 Chemical 
News,’ the result of some very valuable experiments on this 
subject. The arrangement he proposes fully answers the 
purpose ; the crucibles being capable of standing the heat 
of melted wrought iron or cobalt without fusion or cracking, 
as well as of being made of any reasonable size. 

A clay crucible of somewhat larger capacity than the 
desired lime one, is filled with common lamp-black, compres¬ 
ing the same by stamping it well down. The centre is then 
cut out with a knife until a shell or lining of lamp-black 
is left firmly adherent to the sides of the crucible, and about 
half an inch or less in thickness, according to the size of 
the crucibles; this lining is now well rubbed down with a 
thick glass-rod until its surface takes a fine glaze or polish, 
and the whole cavity is then filled up with finely-powdered 
caustic lime, thoroughly pressed down, and a central cavity 
cut out as before; or the lime-powder may be at once 
rammed down round a central core of the dimensions of the 
intended lime crucible. 


122 


ALUMINA CRUCIBLES. 


This lime lining is naturally rather soft before being placed 
in the furnace, but upon heating, agglutinates, and forms a 
strong and compact crucible, which is prevented acting upon 
the outer one by the interposed thin lamp-black layer, and 
at the end of the experiment generally turns out as solid and 
compact as those made in the lathe. 

Experiments made with such crucibles, even up to dimen¬ 
sions containing several pounds of metal, have proved them 
extremely well suited for these operations, and doubtless 
similar crucibles could be made, lined with magnesia or 
alumina as required. In some cases ordinary black-lead 
crucibles, lined with powdered lime, magnesia, or alumina, 
might possibly be found to answer. 

Having frequently used lime crucibles in metallurgical 
operations, and having met with the inconvenience pointed 
out by Mr. Forbes, the writer can appreciate the great value 
of his improvement. It is one which cannot fail to be ex¬ 
tensively adopted in metallurgical laboratories. 

In certain particular experiments, crucibles are lined with 
other bodies besides charcoal and lime, such as silica, alumina, 
magnesia, or chalk, by merety moistening their respective 
powders with water, and applying the paste as above de- 
cribed for the charcoal. A slight layer of chalk lessens the 
liability of attack from fused litharge. 

Alumina Crucibles are strongly to be recommended in 
many metallurgical operations. They are made in the 
following manner. Ammonia alum is ignited at a full red 
or white heat, when it leaves behind pure alumina in a 
dense compact form : this is to be finely powdered. To a 
solution of another portion of ammonia alum in water, 
ammonia is added, when alumina is precipitated in a gela¬ 
tinous state: this is to be washed until free from sulphate 
of ammonia. The dense alumina is then mixed with water 
and worked up into a paste, the precipitated gelatinous 
alumina being kneaded in from time to time ; this gives 
coherency : and when sufficient has been added (which must 
be ascertained experimentally), the mass may be moulded 
into shape. These crucibles require slow and careful drying ; 
but they well repay all the care which is bestowed on them, 


IRON CRUCIBLES. 


123 


for they do not readily crack, are attacked by very few 
fluxes, give out no impurities to metals which are melted 
in them, and are infusible at the highest heat of the furnace. 

Malleable Iron crucibles are often very serviceable in 
assays of fusibility, and of certain selenides and sulphides, as 
in assays of galena or ordinary lead ore. They are either 
made of hammered sheet iron or by plugging up small iron 
tubes, as gun-barrels, &c. The latter are preferable, because 
thick solid crucibles can be used a number of times, whilst 
the others are necessarily very thin and can be used only once. 
Whenever iron crucibles are employed at a very high 
temperature, they must be placed in those of earthenware, 
which protect them from the oxidating action of the air; but 
when they are not heated above the temperature of a copper 
assay, they may be used naked, if tolerably thick. 

For assays at the above temperature, cast-iron crucibles 
may be employed with advantage, instead of wrought-iron, 
because they are very nearly as good, and much less expensive. 

Platinum Crucibles. —Platinum crucibles are invaluable 
in a laboratory. Few pieces of apparatus are used so fre¬ 
quently by the chemist. Their chief use is in the ignition of 
precipitates, and the decomposition of siliceous minerals by 
fusion with alkaline carbonates. They are preferable to 
porcelain, as not being fragile and being more readily heated 
to redness over the gas or spirit flame. Their most con¬ 
venient size is 1J? inch high and 1-^ inch wide at the top. 

In employing a crucible for the incineration of filters in 
quantitative assays by the wet way, it sometimes happens (as, 
for instance, with chloride of silver or sulphate of lead) that 
the employment of platinum is inadmissible. In these cases 
thin porcelain crucibles must be used. The analyst will, how¬ 
ever, frequently experience difficulty, owing to the extreme 
slowness with which, in many cases, the last portions of the 
carbon of a filter are consumed when ignited in a porcelain 
crucible. It does not appear, however, that the following 
simple method of obviating the difficulty—as practised in 
the laboratory of Professor Scheerer, in Freiberg—has ever 
received the publicity which it deserves. Whenever a filter 
upon which a substance capable of injuring platinum has 



124 


PLATINUM CRUCIBLES. 


been collected lias to be incinerated, the porcelain crucible 
or capsule in which the process is to be conducted, should 
be placed within a vessel of platinum of similar form, and 
the whole ignited in the usual way. Whether the greatly 
accelerated rapidity of combustion of the carbon which en¬ 
sues depends upon a more equal distribution of heat brought 
about by the greater conducting power of the metal—an 
explanation which is current for the somewhat analogous 
case of copper-coated glass flasks—or whether, as seems 
probable, the power of the porcelain vessel to absorb heat 
be really increased by the interposition of the platinum; 
whether both these causes be of influence, or the result depends 
upon another less apparent reason ; or finally, whether vessels 
of some other metal would not be preferable to those of 
platinum, are questions which are open to discussion. 

Fresenius gives the following excellent directions as to 
the preservation of platinum crucibles. The analyst should 
acquire the habit of cleaning and polishing the platinum 
crucible always after using it. This should be done, as 
recommended by Berzelius, by friction with moist sea-sand, 
whose grains are all round, and do not scratch. The writer 
has found this method to answer extremely well. The sand is 
rubbed on with the finger, and the desired effect is produced 
in a few minutes. The adoption of this habit is attended 
with the pleasure of always working with a bright crucible, 
and the profit of prolonging its existence. This mode of 
cleaning is all the more necessary, when one ignites over 
gas-lamps, since at this high temperature crucibles soon 
acquire a grey coating, which arises from a superficial 
loosening of the platinum. A little scouring with sea-sand 
readily removes the appearance in question, without causing 
any notable diminution of the weight of the crucible. 

In connection with some sensible remarks upon the above- 
mentioned use of sand in cleaning platinum crucibles, 
Erdmann explains in the following way the cause of the grey 
coating which forms upon platinum crucibles whenever they 
are ignited in the flame of Bunsen’s gas-burner. This 
coating has given rise to much annoyance and solicitude 
among chemists. Indeed it has often been asserted that the 


PLATINUM CRUCIBLES. 


125 


use of Bunsen’s burner is unadvisable in quantitative analysis, 
since by means of it the weight of platinum crucibles is 
altered and the crucibles themselves injured. The coating 
is produced most rapidly when the crucible is placed in the 
inner cone of the flame, and the more readily in proportion 
as the pressure under which the gas is burned is higher. 
Having found it advantageous to maintain, by means of a 
special small gas-holder, a pressure of four or five inches 
upon the gas used in his own laboratory, Erdmann observed 
that the strong gas-flame thus afforded, immediately oc¬ 
casioned the formation of a dull ring upon the polished 
metal placed in the inner flame, this ring being especially 
conspicuous when the crucible becomes red-hot; it increased 
continually, so that after long-continued ignition, the whole 
of the bottom of the crucible was found to be grey and with 
its lustre dimmed. 

This ring is caused neither by sulphur, as some have 
believed, nor by a coating of inorganic matter, but is simply 
a superficial loosening of the texture of the platinum, in 
consequence of the strong heat; whence it first of all appears 
in the hottest part of the flame. In consequence of the 
serious damage which the gas furnace causes, many chemists 
now discard gas and ignite platinum crucibles over specially 
constructed spirit lamps. 

In conjunction with Pettenkofer, Erdmann instituted 
several experiments, which have left but little doubt that the 
phenomenon depends upon a molecular alteration of the 
surface of the metal. If a weighed polished crucible be 
ignited for a long time over Bunsen’s lamp, the position of 
the crucible being changed from time to time, in order that 
the greatest possible portion of its surface shall be covered 
with the grey coating, and its weight be then determined 
anew, it will be found that this has not increased. The 
coating cannot be removed either by melting with bisulphate 
of potash or with carbonate of soda. It disappears, how¬ 
ever, when the metal is polished with sand; the loss of weight 
which the crucible undergoes being exceedingly insignificant, 
a crucible weighing 25 grammes having lost hardly half a 
milligramme. When the grey coating of the crucible is 


V 2 (] PRESERVATION OF PLATINUM CRUCIBLES. 

examined under the microscope, it may be clearly seen that 
the metal has acquired a rough, almost warty, surface, which 
disappears when it is polished with sand. Platinum wires, 
which are frequently ignited in the gas-flame—for example, 
the triangles which are used to support crucibles—become, 
as it is known, grey and brittle. Under the microscope, 
they exhibit a multitude of fine longitudinal cracks, which, 
as the original superficial alteration penetrates deeper, 
become more open, or, as it were, spongy, until, finally, the 
wire breaks. 

If such wire is strongly and perseveringly rubbed with 
sand, the cracks disappear, and the wire becomes smooth and 
polished; for the grains of sand, acting like burnishers, restore 
the original tenacity of the metal, very little of its substance 
being rubbed off meanwhile. The loosening effect of a 
strong heat upon metals is beautifully exhibited when silver 
is ignited in the gas-flame ; a thick polished sheet of silver 
immediately becoming dull white when thus heated. Under 
the microscope the metal appears swollen and warty. Where 
it has been exposed to the action of the inner flame along 
its circumference, this warty condition is visible to the 
naked eye. A stroke with the burnishing stone, however, 
presses down the loosened particles, and reproduces the 
original polish. This peculiar condition which the surface 
of silver assumes when it is ignited, is well known to silver¬ 
smiths ; it cannot be replaced by any etching with acids, and 
it must be remembered that what is dull white in silver, 
appears grey in platinum. 

If each commencement of this loosening is again destroyed, 
the crucibles will be preserved unaltered, otherwise they 
must gradually become brittle. Crucibles of the alloy of 
platinum and iridium are altered like those of platinum, when 
they are ignited. It is, however, somewhat more difficult 
to reproduce the original polish of the metal by means of 
sand, as might be expected, from the greater hardness of the 
alloy. 

The sand used should be well worn. When examined 
under the microscope, no grain of it should exhibit sharp 
edges or corners ; all the angles should be obtuse. 


CLEANING PLATINUM CRUCIBLES. 


127 


It there are spots on the platinum crucibles which cannot 
be removed by the sand without wearing away too much of 
the metal, a little bisulphate of potassa is fused in the crucible, 
the fluid mass shaken about inside, allowed to cool, and the 
crucible finally boiled with water. There are two ways of 
cleaning crucibles soiled outside : either the crucible is placed 
in a larger one, and the interspace filled with bisulphate of 
potassa, which is then heated to fusion; or the crucible is 
placed on a platinum wire triangle heated to redness, and 
then sprinkled over with powdered bisulphate of potassa. 
Instead of the bisulphate borax may be used. Never forget 
at last to polish the crucible with sea-sand again. 

When the crucible is clean, it is placed upon a clear 
platinum-wire triangle, ignited, allowed to cool in the desic¬ 
cator, and weighed. This operation, though not indispens¬ 
able, is still always advisable, that the weighing of the 
empty and the filled crucible may be performed under as 
nearly as possible the same circumstances. 

In using platinum crucibles, it must be remembered that 
certain substances must not be ignited in them. Berzelius 
says, that 4 it is improper to ignite in platinum vessels the 
caustic alkalies or the nitrates of any alkaline base, such as 
lime, baryta, or strontia, because the affinity of the alkali 
lor oxide of platinum, causes a very considerable oxidation 
of the metal; and after the saline matter is removed, the 
surface of the metal is found to be honeycombed.’ 

The alkaline sulphides or the alkaline sulphates mixed 
with charcoal are inadmissible, because the sulphides so 
formed attack platinum even more energetically than the 
caustic alkalies : so are metals whose fusing-point is lower 
than that of platinum, because an alloy would be formed. 
Gold, silver, and copper, may be heated to dull redness in 
platinum vessels without danger; but fused lead cannot 
come in contact with platinum without destroying it. A 
drop of fused lead, tin, zinc, or bismuth, placed on red- 
hot platinum, always produces a hole. Neither can a phos¬ 
phide or phosphoric acid mixed with charcoal be ignited 
m vessels of platinum, b. cause a phosphide of platinum 
is produced, which is an exceedingly brittle compound. 


128 


CUPELS. 


Iii analyses by the humid method, nitro-hydrochloric acid 
(i aqua regia), even when very dilute, must not be allowed 
to come in contact with platinum, and, as a general rule, 
liquids containing either free chlorine, bromine, or iodine, 
must not be boiled in platinum capsules. 

Cupels. —These are vessels in which the operation termed 
cupellation is carried on. They must be made of such 
substances as are not acted upon by certain fused oxides, 
as those of lead or bismuth, and their texture has to be 
sufficiently loose to allow of the oxides penetrating their 
substance readily, and yet be sufficiently strong to bear 
handling without breaking. 

There are several substances of which cupels might be 
made, which will fulfil all these conditions, but only one is 
in general use, viz. the ash of burnt bones. This consists 
principally of phosphate of lime, with a little carbonate and 
some fluoride of calcium. Berzelius found that bones of 
oxen contained 57 parts of phosphate of lime for every 3*8 
parts of carbonate of lime, whilst, according to Barros, sheep 
bones contain 80 parts of phosphate of lime to 19 parts of 
carbonate of lime. When bones are burnt whole they like¬ 
wise contain mineral matter derived from the cartilage, such 
as alkaline sulphates and carbonates. The greater part of 
the carbonate of lime is likewise converted into caustic lime. 

The bones of sheep and horses are best for cupels. In 
getting rid of the organic matter, it is advisable to boil 
them repeatedly in water before burning them. This dis¬ 
solves a great part of the organic matter. If the bones 
are not rendered quite white by the first ignition, but con¬ 
tain a little carbon, they should be ground up, moulded 
into shape, and burned again. 

Care should be taken not to heat the bone earth too 
strongly. In this case the bones will have a smooth, glassy 
fracture, and will not be sufficiently spongy or absorbent 
to make good cupels. 

When the bones are burnt white throughout, they must 
be finely ground, sifted, and washed several times with 
boiling distilled water till all soluble salts are removed. 
The finest particles of the powdered bone earth will remain 


/ 


MANUFACTURE OF CUPELS. 


1-29 


Fig. 60. 


longest suspended in the washing waters. This must be 
allowed to settle separately, and should be reserved for 
gi\ mg a final coating to the surface of the cupels ; this 
coating acts, to a certain extent, like a fine filter, and may 
be applied to all cupels, although the body of the cupel is 
made of different materials. 

h or the body of the cupels, the bone-ash should be about 
as fine as wheat flour. If too coarse, litharge containing 
silver will be absorbed into its pores, and will occasion a 
loss of silver. 

Cupels must neither crack nor alter in texture at a 
white heat. It is very important that they should not con¬ 
tain carbon, and therefore, in making them, the bone-earth 
must not, as sometimes recommended, be mixed with beer, 
or water containing adhesive substances. Nothing but pure 
water should be used, and the mixture should be just suf¬ 
ficiently moist to adhere strongly when well pressed, but not 
so moist as to adhere to the finger or the mould employed to 
fashion the cupels. The mould (fig. GO) con¬ 
sists of three pieces ; one a ring, b , having a 
conical opening ; another a pestle, a, having a 
hemispherical end fitting the larger opening of 
the ring; and the third, c, a piece of turned 
metal, into which b fits ; c serves to form an 
even bottom to the cupel. In order to mould 
the cupels, proceed as follows : Place the 
ring on the lower piece c, and fill it with the 
composition; then place the pestle upon it, and force it 
down as much as possible : by this means the moistened 
bone-ash will become hardened, and take the form of the 
pestle ; the latter must then be driven as much as possible by 
repeated blows from a hammer, until quite home. The 
surface of the cupel may then have sifted over it a little of 
the very fine levigated bone-ash, and the pestle hammered 
again on it. It is then to be turned lightly round, so as 
to smooth the inner surface of the cupel, and withdrawn : 
the cupel is removed from the mould by a gentle pressure 
on the narrowest end. When in this state, the cupel must 

K 




130 


SCORIFIERS. 


be dried gently by a stove ; and lastly, ignited in a muffle, 
to expel all moisture. It is then ready for use. 

There are two or three points to attend to in manufactur¬ 
ing the best cupels. Firstly, the powdered bone-ash must 
be of a certain degree of fineness ; secondly, the paste must 
be neither too soft nor too dry ; and thirdly, the pressure 
must be made with a certain degree of force. A coarse 
powder, only slightly moistened and compressed, furnishes 
cupels which are very porous, break on the least pressure, 
and, as before mentioned, allow small globules of metal to 
enter into their pores. 

When, on the contrary, the powder is very fine, the 
paste moist, and compressed strongly, the cupels have much 
solidity, and are less porous ; the fine metal cannot pene¬ 
trate them, but the operation proceeds very slowly : be¬ 
sides, the assay is likely to become dulled, and incapable of 
proceeding without a much higher degree of temperature 
being employed. 

Cupels for assaying silver bullion are sometimes made of 
equal parts of bone-ash and beechwood-ash; and for 
assaying gold, 2 parts of beechwood-ash, and 1 part of 
bone-ash are used. The hemispherical cavity of both these 
kinds are coated with the fine levigated powder of bone-ash. 

Beechwood-ash is preferred for cupels on account of the 
larger proportion of phosphoric acid it contains. 

According to Hertwig, beechwood-ash contains in 100 
parts:— 


Carbonate of potash.11*72 

Carbonate of soda.12*37 

Sulphate of potash.3*40 

Carbonate of lime ..... 49*54 

Carbonate of magnesia .... 7*74 

Phosphate of lime.3-32 

„ magnesia . . . .2*92 

y, iron.0*76 

„ alumina.1-51 

„ manganese . . . .1*59 

Silica.2*4G 


Scorifiers.— A scorifier (fig. 61) is a vessel made much 
in the shape of a cupel, but of crucible earth. The 
proper use both of cupels and scorifiers will be explained 
under the head of silver assay. 







PYROMETRY. 


131 


Methods op Measuring the Heat of Furnaces. —As 

much of the accuracy of an assay depends on the 
temperature at which it is made, and as the temperature 
required varies with each metal, it is very desirable to 
possess some means of ascertaining the heat of the furnace 
more accurately than by the eye. Many persons have 
devised instruments, called pyrometers, for this purpose ; the 
earliest being those of Mr. Wedgwood and the late Professor 
Daniell, of King’s College. 

We shall not give a description of Wedgwood’s pyro¬ 
meter, as although very ingenious and useful in the absence 
of a better instrument, it has long gone out of use. 


Fro. 61. 



Its indications are very inaccurate, from the fact that the 
clay cylinders, whose contraction serves to measure the 
temperature, will contract as much by the long continuance 
of a low heat as by the short continuance of a high one. 
Hence the degrees of heat measured by Wedgwood’s pyro¬ 
meter have been enormously exaggerated. It was long since 
noticed that it did not produce comparable effects ; and this 
was supposed to proceed wholly from the impossibility of 
obtaining clay perfectly alike for each experiment. 

Daniell’s pyrometer is composed of a rod of platinum 
simply laid in a groove made of refractory clay, and baked 
in the highest degree of heat. This rod rests at one end 
on the edge which terminates the groove, and at the other 
on a lever with two arms, the larger of which forms a 
needle on a graduated arc of a circle; so that the removal 




132 


daniell’s PYROMETER. 


of this needle from its position marks the additional length 
which the metal acquires by the heat. The following is 
Daniell’s description of his pyrometer : 4 It consists of two 
parts (see fig. 62), which may be distinguished as the re¬ 
gister and the scale. The register is a solid bar of black- 
lead or earthenware highly baked. In this a hole is drilled, 
into which a bar of any metal, a , six inches long, may be 
dropped, and which will then rest upon its solid end. A 
cylindrical piece of porcelain, called the index, is then 


Fig. 62 . 




placed upon the top of the bar, and confined in its place by 
a ring or strap of platinum passing round the top of the 
register, which is partly cut away at the top, and tightened 
by a wedge of porcelain. When such an arrangement is 
exposed to a high temperature, it is obvious that the ex¬ 
pansion of the metallic bar will force the index forward to 
the amount of the excess of its expansion over that of the 
black-lead, and that when again cooled it will be left at 
the point of greatest elongation. What is now required is 
the measurement of the distance which the index has been 
thrust forward from its first position, and this, though in 
any case but small, may be effected with great precision by 
means of the scale, c.* 

* Daniell e Chemical Philosophy, p. Ill, 


















daniell’s pyrometer. 


133 


Uiis is independent of the register, and consists of two 
rules oi brass accurately joined together at a right angle 
by their edges, and fitting square upon the two sides of the 
black-lead bar. At one end of this double rule, a small 
plate of brass projects at a right angle, which may be 
brought down upon the shoulder of the register formed by 
the notch cut away for the reception of the index. A 
movable arm is attached to this frame, turning at its fixed 
extremity on a centre, and at its other carrying the arc of 
a circle, whose radius is exactly five inches, accurately 
divided into degrees, and thirds of a degree. Upon this 
arm, at the centre of the circle, another lighter arm is 
made to turn, one end of which carries a nonius with it, 
which moves upon the face of the arc, and subdivides the 
former graduation into minutes of a degree ; the other end 
crosses the centre, and terminates in an obtuse steel point, 
turned inwards at a right angle. When an observation is 
to be made, a bar of platinum or malleable iron is placed 
in the cavity of the register; the index is to be pressed 
down upon it, and firmly fixed in its place by the platinum 
strap and porcelain wedge. The scale is then to be applied 
by carefully adjusting the brass rule to the sides of the re¬ 
gister, and fixing it by pressing the cross piece upon the 
shoulder, and placing the movable arm so that the steel 
part of the radius may drop into a small cavity made for its 
reception, and coinciding with the axis of the metallic bar. 
The minute of the degree must then be noted which the 
nonius indicates upon the arc. A similar observation must 
be made after the register has been exposed to the increased 
temperature which it is designed to measure, and again 
cooled, and it will be found that the nonius has been moved 
forward a certain number of degrees or minutes. The scale 
of this pyrometer is readily connected with that of the 
thermometer by immersing the register in boiling mercury, 
whose temperature is as constant as that of boiling water, 
and has been accurately determined by the thermometer. 
The amount of expansion for a known number of degrees 
is thus determined, and the value of all other expansions 
may be considered as proportionate. 


134 


WILSON’S METHOD OF PYROMETRY. 


By Daniell’s pyrometer tlie melting point of cast iron 
has been ascertained to be 2T8G°, and the highest tempera¬ 
ture of a good wind furnace, 3300° Fahrenheit—points 
which were estimated by Mr. Wedgwood at 17,97/° and 
21,877° respectively. 

The following is a list of the melting points of some of 
the metals as ascertained by Professor Haniell; and it is 
obvious that in an assay of each particular metal the tem¬ 
perature employed must exceed by a con iderable number 
of degrees its melting point. The table is, therefore, very 
useful. 


Tin melts at. 




Fahr. 

. 422° 

Cadmium 




. 442 

Bismuth 




. 407 

Lead .... 




. 612 

Zinc .... 




. 773 

Silver .... 




. I860 

Copper.... 




. 100G 

Gold .... 




. 2016 

Cast iron 




. 2786 

Cobalt and nickel rather less fusible than 

iron. 


Mr. S. Wilson* has described an ingenious process of mea¬ 
suring high temperatures. He exposes a given weight of 
platinum or Stourbridge clay to the action of the heat which 
is to be measured, and then quenches it in a definite weight 
of water at a certain temperature. Thus, if the piece of 
platinum weigh 1,000 grains and the water 2,000 grains at 
60° F., and should the heated platinum when dropped into 
the water raise its temperature to 90°, then, 90° — 60° =30°; 
which, multiplied by 2 (because the weight of the water 
is twice that of the platinum), gives 60°—the temperature 
to which a weight of water equal to the platinum would 
have been raised. To convert this into Fahrenheit degrees 
we must multiply by 31^, which is the specific heat of water 
as compared with platinum, that of the latter being 1. 
Therefore, 60° x 31^=1875°, which will be the temperature 
of the furnace. 

This principle has been very well carried out by 0. 
Bystrom, a captain in the Swedish artillery. His instrument 
is called the hydropyrometer. It consists of two parts, 

* Philosophical Magazine, ser. iv. vol. iv. p. 157. 








BYSTROM S PYROMETER. 


135 


Fig. 63. 


shown in fig. 63. A represents a ball of platinum or other 
metal or alloy, according to the supposed temperature. B 
is a vessel of water. The portion a, a, is of brass, with two 
holes in the upper part; one, A, A, 
for the mixer , and the other, c, c, 
for the mercurial thermometer. 

There is also another hole at the 
lower part, d, by which the water 
is emptied, e , e, is a wooden case 
well screwed together. The mixer 
C consists of a conical ring,/, and 
wires of brass, which connected 
with the lower part of the ring, 
form the small cage, g. The upper 
portion is prolonged into a funnel, 
and lias attached to it a small 
handle, A, used to take hold of and 
turn the mixer. The thermometer 
A, surrounded with the case /, is graduated to show one- 
tentli of a degree Centigrade. 

Fig. 64 shows how the instrument is arranged. Place the 



Fig. 64. 



ball A on the end of the rod C, which is then introduced 
and slid along the two points a, A, to the end of the muffle 
E, through the opening D. Then push the wedge-shaped 





























186 


TIIERMO-ELECTRIC PYROMETER. 


stopper f into this opening, until the rod, which is balanced 
on the point b , touches the point e. Then close the mouth 
D with clay. 

As soon as the ball has acquired the temperature of the 
furnace (in three or four minutes), draw out the rod. The 
ball touching the point e becomes detached and falls, rolling 
down the canal </, k , closed below by the valve /, when it 
falls into the vessel previously filled with a determined 
weight of water, B, through the funnel /. After having closed 
the funnel with a cork, turn the mixer very slowly two 
or three times, slightly shaking the instrument at the 
same time. 

By taking the temperature of the water before ( t ) and 
after ( tf ) the operation, the difference (tf — t) is easily found. 
Reference is then made to the following table (see p. 13/). 

This table is calculated for the weights of 300 grammes 
of water, 7 grammes of steel, and 8 grammes of platinum. 
For each degree tf—t , a temperature x is found to corre¬ 
spond, to which is added the final temperature tf. 


Example 1. 

t' = 17-° 
t = 144 steel 
t’ - t = 2-6 

x the corresponding temperature — G60° 
t' = 17 

the temperature of the furnace 

{x + if) . . . . = G77° 


Example 2. 
tf — 20° 

t = 17 - 75 platinum 
t' - t — 2-25 
.r the corresponding tempera¬ 
ture . . . . = 1550° 

t f .= 20 

the temperature of the furnace 

(x + t') . . . = 1570 


One or two other methods of measuring high tempera¬ 
tures applicable to special cases may here be mentioned. 

Becquerel has proposed a very excellent plan for measur¬ 
ing high temperatures, by means of the thermo-electric 
current generated by heating the junction of two platinum 
wires of different diameters. In a similar manner, the 
thermo-electric current produced by heating two wires of 
platinum and palladium, melted together at one end, has 
been used as a pyrometer. 

A good plan for comparing the temperatures of two 
furnaces is to prepare alloys of platinum and gold, contain¬ 
ing definite quantities, say, 5, 10, 15, 20 % Ac. of gold. 







COMPARISON OF HIGH TEMPERATURES. 


137 


X 

f 

- t 

X 

t' - t 

X 

t' - t 

Temperature 

centigrade 

Steel 

Platinum 

Temperature 

centigrade 

Platinum 

Temperature 

centigrade 

Platinum 

300 

0-89 

0-26 

920 

0-97 

1520 

2-17 

50 

1-08 

•30 

40 

1-00 

40 

•22 

400 

•27 

•35 

50 

•01 

50 

•24 

50 

•49 

•40 

60 

•03 

60 

•27 

500 

•72 

•45 

80 

•06 

80 

•32 

50 

•97 

•50 

1000 

•09 

1600 

•38 

000 

2-24 

•56 

20 

•12 

20 

•44 

20 

•36 


40 

•15 

40 

•50 

40 

•48 


50 

•16 

50 

•53 

50 

•54 

•62 

60 

•18 

60 

•56 

60 

•60 


80 

•21 

80 

•62 

80 

•73 


1100 

•25 

1700 

•68 

700 

•86 

•68 

20 

•29 

20 

•74 

10 

•92 


40 

•33 

40 

•80 

20 

•98 


50 

•35 

50 

•83 

30 

3*05 


60 

•37 

60 

•86 

40 

•12 


80 

•41 

80 

•92 

50 

•19 

•74 

1200 

•45 

1800 

•99 

00 

•26 


20 

•49 

20 

3-06 

70 

•34 


40 

•53 

40 

•13 

80 

•42 


50 

•55 

50 

•16 

90 

•50 


60 

•57 

60 

•20 

800 

•58 

o 

GO 

• 

80 

•61 

80 

•27 

10 

•66 


1300 

•65 

1900 

•34 

20 

•74 

do 

to 

20 

•69 

20 

•41 

30 

•82 


40 

•73 

40 

•48 

40 

•90 

•85 

50 

•75 

50 

•51 

50 

•98 

•86 

60 

•77 

60 

•55 

CO 

4-07 

•88 

80 

•82 

80 

•62 

70 

•16 


1400 

•87 

2000 

•70 

80 

•25 

•91 

20 

•92 



90 

•34 


40 

•97 



900 

•43 

•94 

50 

1-99 



5 

•47 


60 

2-02 



10 

•52 


80 

•07 



15 

•57 


1500 

•12 




Observation .—x -f- t r is tbe temperature of the furnace. 


These fuse at intermediate temperatures between gold and 
platinum. By placing small angular chips of these alloys 
separately in muffles, and noticing which are melted, which 
softened only, and which resist the action of the heat, an 
idea of the power of the furnace is obtained. In this way 
the amount of heat required to perform any operation may 
be registered for future reference, by simply recording that 
it was sufficient just to melt, say a 20 gold 80 platinum 
alloy. 




















































138 


CHAPTER V. 


FUEL : ITS ASSAY AND ANALYSIS. 


Before treating of the assay of metals and metalliferous 
ores, it is advisable to devote some space to the important 
subject of fuel. The substances employed as fuel, although 
all of vegetable origin, are derived either from the vegetable 
kingdom (wood), or from the mineral kingdom (peat, brown 
coal, coal, anthracite). These natural fuels can be con¬ 
verted into artificial fuels by heating them more or less out 
of contact with the air (charcoal, turf-charcoal, coke). 

The essential elements of combustible matters are carbon, 
oxygen, and hydrogen ; nitrogen being present sometimes, 
but only in small proportions. These constitute the organic 
part; various salts and silica constitute the inorganic part, 
or ash. The valuable constituents of fuel, on which its 
calorific and reducing powers depend, are the carbon and 
hydrogen, and it is upon the combustion or union of these 
elements with oxygen to form carbonic acid and water, that 
the effect of the fuel depends. 

The more oxygen a fuel contains the less carbon and 
combustible gases it will yield, and the more hydrogen, the 
more combustible gases. 


The proportion of hydrogen to oxygen in wood 


a 

a 

a 

turf 

it 

it 

it 

fossil-wood 

a 

a 

a 

coal 

a 

tt 

a 

anthracite 


is 

a 

a 

it 

it 


1 : 7 
1 : G 
l : 4 
1 :2-3 
1 :1 


The more oxygen, the less carbon the fuel contains, thus : 


Anthracite contains about 
Coal „ 

Brown coal „ 
Fossil-wood and turf 
Wood 


it 


a 

tt 

a 

tt 


90% carbon 


80 „ 
70 „ 
(50 „ 
50 „ 


a 

tt 

tt 

a 


ASSAY OF FUEL. 


139 


The more carbon a fuel contains, the greater heat it pro¬ 
duces, and the more difficult it is to ignite. 

T he greater the amount of hydrogen in a fuel, the more 
inflammable it will be, and the larger flame it gives, the 
hydrogen being evolved below a red heat. But the more 
carbon present, the less flame. These differences are shown 
in a blazing fire and a glowing fire. In a flame the hottest 
part is at the periphery, whilst in a glowing fire the greatest 
heat is in the immediate contact of the burning surface. 

The assay of fuel comprises the following examinations : 

1. The examination of the external appearance of the 
fuel, its porosity or compactness, its fracture, the size and 
shape of the pieces composing it. 

2. Determination of the adhering water. 

3. The specific gravity. 

4. Determination of the absolute heating power. 

5. Determination of the specific heating power. 

6. Determination of the pyrometric heating power. 

7. Determination of the volatile products of carbonisa¬ 
tion. 

8. Examination of the coke or charcoal left behind on 
carbonisation, both with regard to quality and quantity. 

9. Determination of the amount of ash, and its compo¬ 
sition. 

10. Determination of the amount of sulphur. 

11. Examination of any other peculiarity which may 
be noticed during the burning or carbonisation of the fuel. 

1. External Appearance op the Fuel, its Porosity, 
Compactness, Fracture, Size, and Shape of Pieces. —From 
the outward appearance of a fuel, its cleavage, and an ex¬ 
amination of the embedded earthy matter, iron pyrites, 
gypsum, &c., its applicability to any special purpose may 
be judged. Its degree of inflammability, together with the 
pressure of blast which it will bear in the furnace, partly 
depends on the more or less compactness of the fuel. The 
amount of loss which it will suffer in transport depends 
upon its friability. Playfair and De la Beche * determined 

* Dingl. cx. 212 , 263 ; cxiv. 346 . Liebig’s 1 Jahresber.,’ 1847 - 1848 , p . 1117 
1849 , p . 708 . 


140 


ASSAY OF FUEL. 


the amount of this loss in coal by rotating in a barrel dif¬ 
ferent qualities of coal for the same time. The powder 
produced was separated and weighed, and in this way the 
friability or cohesion of a fuel could be expressed in per¬ 
centages. Schrotter * made the same experiments with 
brown coal. 

The size and form of the pieces composing the fuel is 
important, as on this depends the space occupied in its 
stowage—an important point for steam-vessels. This space 
cannot be calculated from its specific gravity, but must be 
ascertained by direct measurement. The space occupied 
will be smallest when the form of the lumps is cubical. 
Playfair and De la Beche have also investigated this subject. 

2. Determination op the Adhering Water.— The water 
contained in a fuel exerts great influence on its heating 
power. It not only increases its bulk, but it acts injuri¬ 
ously by abstracting a’certain quantity of hdat required for 
its evaporation, and it also causes imperfect combustion. 
For this reason, wood, turf, and brown coal never give so 
high a temperature as coal, anthracite, and coke. 

The determination of the adhering water is effected by 
drying a certain weight of the pounded fuel in a water-bath 
at 212° F. or in an air-bath at 220°. It may also be ascer¬ 
tained by placing a certain weight of the powdered fuel in 
a glass tube, heating to 212°, and passing over it air dried 
by means of chloride of calcium, till the fuel no longer loses 
weight. The amount of water which the dried fuel will 
absorb from the atmosphere in twenty-four hours, should 
also be determined, in order to ascertain its hygroscopic 
qualities. 

3. Determination of the Specific Gravity. —The specific 
gravity of a fuel depends on its density and the amount of 
ash, and it appears also to be in proportion to its greater 
or less inflammability. Of two equal volumes of carbonised 
fuel, the one will produce the greatest heating effect which 
has the greatest specific gravity, provided the density is not 
produced by mineral constituents. 

* Wien. akad. Ber. 1840, Nov. and Dec. p. 240. Liebig’s ‘ Jahresber.,’ 1840. 
p. 700. 


ASSAY OF FUEL. 


141 


The determination of the specific gravity is difficult, and 
sometimes uncertain, owing to the cleavage of the fuel, and 
the entanglement of air in its pores. The best way of 
obviating this difficulty, is to finely powder the fuel before 
taking its specific gravity. Full directions will be found in 
a subsequent chapter. 

4. Determination op the Absolute Heating Power.— 

The value of a fuel for any purpose depends chiefly on 
its price and the quantity required for that purpose. The 
quantity required depends on the heating power possessed 
by a certain weight of fuel (its absolute heating power) or 
that possessed by a certain volume (its specific heating 
power). 

The less oxygen, ash, and water the fuel contains, the 
greater its heating power will be, and this will also in¬ 
crease in proportion to the carbon and hydrogen present. 

Whether the combustion is effected quickly or slowly, the 
amount of heat produced will be the same, but the degree 
of temperature attained will be very different. This latter 
constitutes the pyrometric heating power. 

The determination of the absolute heating power of a fuel 
may be effected,— 

a. By heating a definite quantity of water from 32° F. to 
212 °; 

b. By ascertaining how much fuel is required to melt a 
known weight of ice ; 

c. By ascertaining how much water may be evaporated 
by 1 lb. of different kinds of fuel ; 

d. By ascertaining how much the temperature of a room 
increases by burning a certain weight of a fuel in a stove. 

e. By ascertaining the elementary composition of the 
fuel, and calculating how much oxygen will be required to 
convert the carbon and hydrogen into carbonic acid and 
water; the quantity of heat produced will be in proportion 
to the amount of oxygen consumed. 

f. By Berthier’s method, 

<j. By Dr. Ure’s method. 

According to Berthier, the most convenient method 



142 


bertiiier’s method for assay of fuel. 


for ascertaining the comparative calorific power of any 
combustible matter is by means of litharge. He says: 
It has been proved by the experiments of many philoso¬ 
phers, that the quantities of heat emitted by combustible 
substances are exactly proportioned to the amounts of 
oxygen required for their complete combustion. Whence, 
after the elementary constitution of any combustible is 
known, its calorific power is easily determined by calcula¬ 
tion. For instance, it is only necessary to ascertain the 
quantity of oxygen absorbed in the conversion of all its 
carbon into carbonic acid, and all its hydrogen into water, 
and compare that quantity with that which is consumed in 
burning a fuel whose calorific power is well ascertained. 
Such a substance is charcoal. 

By adopting the principle just pointed out, it may be 
conceived that, without knowing the composition of a fuel, 
its heating power may be ascertained by determining the 
amount of oxygen it absorbs in burning. This can be 
done in a very simple and expeditious manner, if not ex¬ 
actly, at least with sufficient exactitude to afford very useful 
results in practice. It is as follows : many metallic oxides 
are reduced with such facility that when heated with a com¬ 
bustible body, the latter burns completely, without any of 
its elements escaping the action of the oxygen of the oxide, 
if the operation be suitably performed. The composition 
of the oxide being well known, if the weight of the part 
reduced to the metallic state be taken, the quantity of oxygen 
employed in the combustion can be ascertained. In order 
to collect the metal and separate it from the non-reduced 
mass*it must be fusible as well as its oxide. Litharge fulfils 
these conditions, and experiment has proved that it com¬ 
pletely burns the greater part of all ordinary fuels ; the only 
exceptions are some very bituminous matters containing a 
large proportion of volatile elements, a portion of which 
escapes before the temperature is sufficiently high to allow 
the reduction to take place. The experiment is made as 
follows:—10 grains of the finely-powdered, or otherwise 
divided fuel is mixed with about 400 grains of litharge. 
The mixture is carefully placed in an earthen crucible, and 


BERTIIIER’s METHOD FOR ASSAY OF FUEL. 143 

covered with 200 grains more litharge. The crucible is 
then placed in the fire and gradually heated. When the 
fusion is perfect, the heat is urged for about ten minutes, in 
order that all the lead may collect into a single button. 
The crucible is then taken from the fire, cooled, broken, 
and the button of lead weighed. Sometimes the button is 
livid, leafy, and only slightly ductile ; in which case it has 
absorbed a little litharge. This can be partially prevented 
by fusing slowly, and adding a little borax. 

Two assays, at least, ought to be made, and those results 
which differ more than a grain or two ought not to be 
relied on. The purer the litharge, the better the result; it 
ought to contain as little minium as possible. It is an ex¬ 
cellent plan to mix up the litharge of commerce with one 
or two thousandths of its weight of charcoal, and fuse the 
whole in a pot; when cold, pulverise the litharge, which will 
now be deprived of minium. 

Pure carbon produces, with pure litharge, thirty-four 
times its weight of lead, and hydrogen 103*7 times its 
weight of lead ; that is to say, a little more than three 
times as much as carbon. We can, therefore, from these 
data, find the equivalent of any fuel, either in carbon or 
hydrogen. 

When a fuel contains volatile matters, the quantity can be 
ascertained, as before pointed out, by ignition in a close 
tube or crucible. If, further, we ascertain the proportion of 
lead it gives with litharge, it is easy to calculate the equiva¬ 
lent in carbon of the volatile matters, and, in consequence, 
to ascertain its calorific value. 

Supposing that a substance gives by distillation C parts of 
coke, or carbon, having deducted the weight of the ash and 
of volatile substances, and that it produces P parts of lead 
with litharge. The quantity C of carbon would give 34 x C 
of lead ; the quantity of volatile matter would give but 
P — 34 x C; it would be equivalent to F ~ 34 — of carbon: 
whence it follows that the quantity of heat developed by 
the charcoal, the volatile matter, and the unaltered com¬ 
bustible, will be to each other as the numbers 34 x C, 
P — 34 x C, and P. 



144 


DU. URE ON BERTIIIER’S METHOD. 


Dr. Ure * says, speaking of the above method of assay, 
4 On subjecting this theory to the touchstone of experi¬ 
ment, I have found it to be entirely fallacious. Having 
mixed very intimately 10 grains of recently calcined char¬ 
coal with 1000 parts of litharge, both in fine powder, I 
placed the mixture in a crucible, which was so carefully 
covered as to be protected from all fuliginous fumes, and 
exposed it to distinct ignition. 

4 ISTo less than 603 grains of lead were obtained, whereas, 
by Berthier’s rule, only 340 or 346 6 were possible. On 
igniting a mixture of 10 grains of pulverised anthracite 
with 500 grains of pure litharge previously fused and 
pulverised, I obtained 380 grains of metallic lead. In a 
second experiment, with the same anthracite and the same 
litharge, I obtained 450 grains of lead ; and in a third, 
only 350 grains. It is therefore obvious that this me¬ 
thod of Berthier’s is altogether nugatory for ascertaining 
the quantity of carbon in coals, and is worse than useless 
in judging of the calorific qualities of different kinds of 
fuel.’ 

This discrepancy in the results obtained by Dr. Ure is very 
perplexing, and does not at all accord with Berthier’s ex¬ 
perience, as shown by his experiments, or by the author’s, on 
tire subject. The latter never had a difference of more than 50 
grains, and in general only two or three, which latter result 
is satisfactory. The only precaution he found necessary was 
to heat very gradually until the mixture was fully fused, 
and then to increase the fire to bright redness for a few 
minutes. 

Further experiments have been made by the author on 
this subject, and he has succeeded most perfectly in estimat¬ 
ing the value of a fuel. With the litharge of commerce, 
which contains much minium, the process is never exact: 
results have been obtained differing as much as 40 or 50 
grains when the litharge employed had not been purified, 
and to purify it completely is a troublesome process. This 
difficulty may be completely obviated, however, by substi¬ 
tuting for litharge, white lead, using for each 10 grains of 

* 4 Supplement to the Dictionary of Arts, Mines, and Manufactures.’ 


ure’s calorimeter. 


145 


fuel i 00 grains of white lead, which are well mixed with it, 
and 300 grains of pure white lead to cover the mixture. 
W hen the whole is heated, the carbonate of lead decomposes, 
forming pure oxide of lead, which is then reduced, as in 
the former case. By this process the residts correspond 
to 1 grain in the quantity of lead produced from a given 
sample of fuel. Of course great care must be taken that 
the white lead is genuine. 

Commercial samples are frequently adulterated with sul¬ 
phate of lead and sulphate of baryta, oxychloride of lead, 
oxide of zinc, &c. This is a serious drawback to this other¬ 
wise excellent modification. 

The following is the method of ascertaining the calorific 
power of fuel, employed by Dr. Ure, and described in his 
‘Supplement.’ 

4 The following calorimeter, founded upon the same prin¬ 
ciple as that of Count Bumford, but with certain improve¬ 
ments, may be considered as an equally correct instrument 
for measuring heat with any of the preceding (Lavoisier, 
Meyers, and others), but one of much more general appli¬ 
cation, since it can determine the quantity of heat disen¬ 
gaged in combustion, as well as the latent heat of steam and 
other vapours. 

4 It consists of a large copper bath capable of holding 100 
gallons of water. It is traversed four times backwards and 
forwards in four different vessels, by a zigzag horizontal flue 
or flat pipe, nine inches broad and one deep, ending below in 
a round pipe, which passes through the bottom of the bath, 
and receives there into it the top of a small black-lead fur¬ 
nace, the innermost crucible of which contains the fuel. It 
is surrounded at the distance of an inch by a second crucible, 
which is enclosed at the same time by the sides of the 
outermost furnace, the strata of stagnant air between the 
crucibles serving to prevent the heat being dissipated into the 
atmosphere by the body of the furnace. A pipe from a 
double pair of bellows enters the ashpit of the furnace at 
one side, and supplies a steady but gentle heat to carry on 
the combustion kindled at first by half an ounce of burning 
charcoal. So completely is the heat which is disengaged by 

L 


146 


ike’s CALORIMETER. 


the burning fuel absorbed by the water in the bath, that the 
air discharged at the top pipe is generally of the same tem¬ 
perature as the atmosphere. The vessel is made of copper, 
weighing 2 lbs. per square foot; it is 5^ feet long, 1 \ wide, 
2 deep, with a bottom 5^ feet long, and 11 broad upon an 
average. Including the zigzag tin-plate flue, and a rim of 
wrought iron, it weighs altogether 85 lbs. Since the specific 
heat of copper is to that of water as 94 to 1000, the specific 
heat of the vessel is equal to that of 8 lbs. of water; for 
which, therefore, the exact correction is made by leaving 
8 lbs. of water out of the 000 or 1000 lbs. used in the ex¬ 
periment. 

‘In the experiments made with former calorimeters of 
this kind, the combustion was maintained by a current or 
draught of a chimney open at bottom, which carried off at 
the top orifice of the flue a variable quantity of heat, very 
difficult to estimate. 

c The heating power of the fuel is measured by the num¬ 
ber of degrees of temperature, which the combustion of 1 lb. 
of it raises 600 or 1000 of water in the bath, the copper 
substance of the vessel being taken into account. 1 lb. of 
dry wood charcoal, by its combustion, causes 6000 lbs. of 
water to become 20° hotter. For the sake of brevity, we 
shall call this calorific energy 12,000 unities. In like cir¬ 
cumstance, 1 lb. of Llangennock coal will yield by combus¬ 
tion 11,500 unities of caloric.’ 

This form of calorimeter of Dr. Ure’s seems to possess many 
advantages over Laplace’s and others, and is, no doubt, very 
convenient in use, although rather bulky. 

The instrument known as Wright’s calorimeter gives very 
accurate residts, and is the one most generally used now in 
experiments on the heating power of fuel, in all but the most 
refined investigations. It is shown in the accompanying 
figure. 

The copper cylinder A B is filled with a mixture of 20 
grains of the combustible, and 240 of the deflagrating com¬ 
pound, which is composed of three parts of chlorate of potash, 
and one of nitrate of potash. A little piece of cotton soaked 
in chlorate of potash is placed partly in the mixture, the other 


WRIG Ill’s CALORIMETER. 


147 


end projecting above the top of the cylinder ; this is ignited, 
quickly coy ered with the bell-shaped partof the apparatus, and 
immersed in a measured quantity, of water. As constructed, 


Fig. 65. 



Dimensions. 

AB=n3| in.; diameter | in. 

CD = 2 in. 

CB, socket for AB. 

Diameter across D=4 in. 

EF = f> in. 

FG = f» in.; diameter HG = 1| in. 

AB weighs 39J grammes. 

The remainder of the apparatus, including 
the stop-cock, weighs 391 grammes. 



Scat.e of 12 Inches. 


the whole metallic apparatus weighs 0642*7 grains, and with 
this weight 290*1 grains of water are used. The temperature 
is recorded before and after making the experiment. During 
the deflagration the stop-cock is closed, which is, however, 
opened before taking the temperature the second time. A 












14S 


PYROMETRIC EXAMINATION OF FUEL. 


tentli of the temperature that the water is raised by the com¬ 
bustion, is added for errors that are incidental to the use 
Of the instrument. 

If the instrument is made of the weight above given, the 
result is obtained by a very simple calculation. Each Fah¬ 
renheit degree by which the temperature of water has been 
augmented, corresponds to a pound of water converted into 
steam. 

I'U' 

EXAMPftE.i 

. Fahr. 

Temp, of water before making experiment = .56° 

„ „ after the combustion . = _65 

9° -f y 5 th 

„ produced by the combustion = 9-9 


20 grains of the coal will convert into steam (maximum effect) 9-9 lbs. of water 


9-9 x 7000 x 2240 
20 


Effect of a ton. 


5. Determination of the Specific Heating Power.— 

This represents the heat produced from a certain volume 
of fuel. It may be ascertained by multiplying the absolute 
heating power by the specific gravity. 

6. Determination of the Pyrometric Heating Power.— 
By pyrometric heating power is meant the degree of 
temperature which may be obtained by completely burning 
the fuel. This heating power not only depends upon the 
composition of the fuel, but chiefly on the time required for 
its combustion, and this again depends on the looseness and 
inflammability of the fuel. The absolute heating power of 
hydrogen is greater than that of carbon, but with regard 
to the pyrometric heating power it will be found that 
reverse is the case. 

Carbon burned in contact with the air to carbonic acid 
will produce a heat of 2558° C. ; if burned to carbonic 
oxide it only produces 1310°; hydrogen burning to water 
will produce a heat of 2080°. From this we learn that 
fuel rich in carbon, such as anthracite, coal, and coke, will 
produce a greater pyrometric effect than fuel rich in hydro¬ 
gen, as wood, &c. 

Density is an essential quality of fuel required to pro- 



ASSAY OF FUEL. 


149 


duce great pyrometric effect. This is proved in the follow¬ 
ing way. 

When atmospheric air first acts on the carbon contained 
in fuel, carbonic acid is formed, and the temperature rises 
to a certain degree, but on passing over glowing coal, car¬ 
bonic acid becomes converted into carbonic oxide, and this 
causes a portion of the heat at first produced to become 
latent. This conversion of carbonic acid into carbonic 
oxide is more easy and complete, as the fuel used is more 
inflammable; and as a greater quantity of heat is thereby 
rendered latent, it follows that the heating power of such a 
fuel is inferior. This accords with general experience ; for 
it is well known that coke is able to produce a greater heat 
than charcoal. 

Several good methods for determining pyrometric heating 
power were given in the last chapter. 

7. Determination of the Volatile Products of Carboni¬ 
sation. —The amount of volatile matter yield on carbonising 
a fuel depends partly on the composition of the fuel, and 
partly on the temperature employed. If a fuel rich in 
oxygen and hydrogen is quickly heated, it will yield the 
greatest amount of volatile products. These are partly 
liquid (tar, naphtha, and acetic or ammoniacal water), and 
partly gaseous (carbonic oxide, carbonic acid, and light and 
heavy carburetted hydrogen). The more oxygen a fuel 
contains, the more carbonic acid and carbonic oxide it will 
produce; the more hydrogen it contains, the more illumi¬ 
nating gas it yields. The applicability of a sample of coal 
to the production of illuminating gas depends on these 
conditions. 

Coal distilled at a low temperature yields much tar and 
comparatively little gas, and when a very high temperature 
has been used, less tar and more gas is produced, but the 
great heat will have reacted on the gas and injured its illu¬ 
minating qualities. If the coal contains pyrites, the gas will 
contain sulphur compounds. The amount of water pro¬ 
duced is generally larger than that of the tar. 

In order to estimate the amount of volatile matter 
given off from any particular sample of coal, proceed in the 


150 


EXAMINATION OF COKE OF FUEL. 


following manner:—Place a given weight, say 200 grains, 
of the coal in an iron tube, closed at one end, to the other 
end of which adapt, by means of a cork, a glass or other 
tube, which must be conducted into an inverted jar full of 
water standing in the pneumatic trough. Eaise the tem¬ 
perature very gradually to redness, and continue the heat 
until no more gas is given off, then ascertain its quantity 
in cubic inches, with due correction for temperature and 
pressure. 

8. Examination of the Coke or Charcoal left behind on 

Carbonisation _The amount of coke or charcoal yielded by 

a sample of fuel is found by the last operation. The residue 
is the amount of coke which that particular sample of coal 
produces ; and its weight, divided by two, gives the per¬ 
centage of coke. 

The process of coking, charring, or carbonising fuel, 
whilst it drives off some of the valuable hydrocarbon con¬ 
stituents, also gets rid of all the aqueous elements. And, 
therefore, the coke or charcoal which is left behind has its 
value greatly increased when high temperatures are required, 
although, from the absence of flame-yielding constituents, it 
is much more difficult to ignite. 

The degree of inflammability of coke or charcoal is rela¬ 
tively the same as that of the raw fuel from which they 
were produced. The more inflammable a fuel has been, 
the more inflammable will be the coke or charcoal produced 
from it. 

The temperature employed in the carbonisation, as has 
been already explained, exerts great influence on the yield 
of coke. 

If the fuel contains iron pyrites, part of the sulphur goes 
off in the volatile portion, but from \ to \ is retained in the 
form of FeS. 

1). Determination of the Amount of Ash. _In order to 

ascertain the amount of ash :—Fully ignite about 50 grains 
of coal in a platinum capsule, allowing the air to have free 
access all the time until nothing but ash is left. Its amount 
may then be ascertained by weighing: good fuel should 
contain little ash. It may vary from I to 10 per cent., 



DETERMINATION OF SULPHUR IN FUEL. 


151 


but it it exceeds 5 per cent., it becomes deleterious. The 
chemical composition of the ash also influences the quality 
of the fuel to some extent. 

10. Determination of the Amount of Sulphur. —This is an 
important operation in the assay ; as a coal containing sul¬ 
phur cannot be employed for particular operations, and, 
indeed, those which contain much sulphur ought only to be 
used for the commonest purposes. This assay is most im¬ 
portant to steamboat and other companies, who consume 
fuel under steam-boilers; and the coal they purchase should 
always be subjected to this particular test, as sulphur has 
a corroding and destroying action on iron and copper. 
Where sulphurous coals are continually burnt under boilers, 
the metal of the latter becomes deteriorated, and the 
boiler is rapidly rendered useless. Sulphur exists in 
coal in the form of iron pyrites ; these can generally be 
detected by their brassy colour. Some coals and lignites 
also contain sulphate of lime, and in rare cases sulphate of 
baryta. 

The process for the determination of the amount of sul¬ 
phur in coal is not difficult. 1 part of the coal is to be 
finely pulverised, and then mixed with 7 or 8 parts of 
nitrate of potash, 16 parts of common salt, and 4 parts of 
carbonate of potash, all of which must be perfectly pure; 
the mixture is then placed in a platinum crucible and gently 
heated. At a certain temperature, the whole ignites and 
burns quietly. The heat is then increased until the mass is 
fused : the operation is finished when the mass is white. 
It must, when cold, be dissolved in water, the solution 
slightly acidulated by means of hydrochloric acid, and 
chloride of barium added to it as long as a white precipitate 
forms. This precipitate is sulphate of baryta, which must 
be collected on a filter, washed, dried, ignited, the filter 
burnt away, and the remaining sulphate of baryta weighed : 
every 116 parts of it indicate 16 of sulphur. 

Dr. Price has drawn attention to a source of error which 
has hitherto escaped notice in the estimation of sulphur, 
where fusion of the substance with nitre is the process em 
ployed. This author has found that unless great care be 


152 


ASSAY OF FUEL. 


taken to prevent the fused mass passing over to the outside 
of the vessel, and so coming in contact with the flame, or 
products of combustion, an appreciable and, in some cases, 
serious error will arise, owing to the sulphuric acid pro¬ 
duced from the sulphurous acid in the flame—a product of 
the oxidation of the sulphide of carbon contained in the gas 
—combining with the potash of the fused salt. Several 
experiments have been made to ascertain the amount of 
error that may be occasioned from the above cause. In 
one instance, the flame issuing from a Bunsen’s burner was 
made to strike against a little fused nitre on the underside 
of a small platinum dish, when, in three quarters of an 
hour, as much sulphuric acid was obtained as is equivalent 
to 12 milligrammes of sulphur. As a check on these ex¬ 
periments, nitre was fused by the flame of the spirit lamp, 
when, as was to be anticipated, not a trace of sulphuric acid 
could be detected upon the addition of a barium-salt to the 
aqueous solution of this fused mass, rendered acid by hydro¬ 
chloric acid. In determinations of sulphur in coke or coal, 
great care should, therefore, be taken to prevent any of the 
fused saline contents of the crucible from getting on to the 
outside. In fusing pig-iron with nitre, a process recom¬ 
mended by some for the estimation of the sulphur it con¬ 
tains, the mass, especially if the iron be rich in manganese, 
invariably creeps over to the outer wall of the crucible ; and 
it is, therefore, impossible to obtain correct results when the 
operation is conducted over the gas flame. The analyst 
should for these reasons always employ a spirit flame in 
preference to gas in sulphur determinations. 

There is another process for the estimation of sulphur 
which is sometimes adopted, as it is quicker and less 
troublesome than the above ; this is by oxidising the coal 
by boiling it in nitric acid, instead of fusing it with nitre. 
Mr. Crossley* has, however, shown that this plan gives very 
incorrect results. 

IT Examination of other Peculiarities of Fuel.— 

Besides the above-named examinations, the assayist should 


* Chemical News } May 18G2. 


ASSAY OF FUEL. 


153 


notice the degree of inflammability of the fuel, and whether 
any particular smell is evolved during combustion; whether 
the coal is good for coking purposes; whether it burns 
with a large smoky flame or a luminous flame ; whether it 
burns quietly or with decrepitation ; and whether the ash is 
dusty or fusible, and likely to accumulate and clog up the 
grate bars. 


154 


CHAPTER VI. 

REDUCING AND OXIDISING AGENTS—FLUXES, ETC. 

In some of the operations in the dry way, bodies are heated 
in suitable vessels per se ; but it is more often necessary to 
add to the bodies submitted to assay other substances, which 
are varied according to the nature of the change to be ef¬ 
fected. These substances may be divided into five classes:— 

I. reducing agents; II. oxidising agents ; III. desulphurising 
agents ; IV. sulphurising agents; and lastly, V. lluxes pro¬ 
perly so called. 

I. REDUCING AGENTS. 

The substances belonging to this class have the power 
of removing oxygen from those bodies with which it may 
be combined. In assaying, the substance under examination 
is generally fully oxidised either naturally or artificially, 
before reduction is required to be effected. The most 
common reducing agents are as follows :— 

1. Hydrogen gas. 

2. Carbon. 

3. The fat oils, tallow, pitch, and resins. 

4. Sugar, starch, and gum. 

5. Tartaric acid. 

6 . Oxalic acid. 

7. Metallic iron, and lead. 

Hydrogen Gas. —The most common method of prepar¬ 
ing this gas consists in dissolving zinc in dilute sulphuric 
acid. But as this plan gives the gas in the moist state, 
it must be dried, by being allowed to bubble through 
oil of vitriol or by being passed through a bottle containing 
fragments of dried chloride of calcium, before it is used 
loi assaying puiposes. This gas will only be required in very 




REDUCING AGENTS. 


155 


accurate assays, which are generally performed where there 
are ample conveniences for generating pure hydrogen 
gas. The gas is inodorous, invisible, and colourless, when 
absolutely pure. It is a most powerful reducing agent, and 
reduces a great number of metallic oxides at a red or white 
heat; viz. the oxides of lead, bismuth, copper, antimony, iron, 
cobalt, nickel, tungsten, molybdenum, and uranium. When 
any metal is required in a state of absolute purity, this is 
the only reducing agent admissible, as others give the 
metal combined with a certain proportion of carbon. 

Carbon.— Found in large quantities in the mineral king¬ 
dom, but generally combined with other bodies. In a per¬ 
fect state of purity, it constitutes the diamond. The diamond, 
like all other species of carbon, is unacted on by the 
highest possible temperature when in close vessels. It burns 
in atmospheric air and oxygen gas, but requires for com¬ 
bustion a higher temperature than ordinary charcoal. After 
the diamond, the varieties of carbon found in nature or 
artificially prepared, are :— 

Firstly, Black-lead or Graphite.— This is a mineral found 
in beds in the primitive formations, principally in granite 
and mica-schist. It is generally mixed with earthy sub¬ 
stances, and rarely yields less than 10 per cent, of ash. 
Before employing it for reduction purposes it should be 
purified. Lowe * has given an excellent plan for effecting 
this object. 

Secondly, Anthracite. —Which is another species of fossil 
carbon much resembling ordinary coal, but differing from 
it by burning with neither smell, smoke, nor fame. 

Thirdly, Coke.— Which is the residue of the coal employed 
in the gas-works after all the volatile matter is expelled. It 
is generally iron black, and has nearly a metallic lustre ; it 
is difficult to inflame, and burns well only in small pieces, 
but gives a very intense heat. Oven or furnace coke is pre¬ 
ferable, as it is harder, lasts longer, and is more economical 
in use. 

Fourthlv, Wood Charcoal. —Which is obtained by burning 
the woody part of plants, with a limited supply ol air, so 

* Polyt. Centr. 1855, p. 1404. 




REDUCING AGENTS. 


1£G 


as to drive off all their volatile matters, and leave merely 
their carbon. It is this kind that is generally employed 
in assays. It ought to be chosen with care, well pulverised, 
passed through a sieve, and preserved in well-stopped vessels. 
Wood charcoal is never perfectly pure, generally containing 
a proportion of hydrogen and watery vapour: these bodies 
are not generally prejudicial, but in some experiments they 
ought not to be present: in that case, pure charcoal may be 
procured by heating sugar to redness in a close crucible. 

The advantage of carbon as a reducing agent consists in 
its great affinity for oxygen, which at a red heat surpasses 
that of most other substances. Charcoal by itself possesses 
two inconveniences: firstly, it has the property of combining 
with many metals; and in the second place, it is infusible, 
and cannot combine with vitreous substances. The pro¬ 
perty it possesses of combining with iron, nickel, cobalt, 
&c., is of no consequence to the assayer, for the increase of 
weight it gives is not material, excepting under the circum¬ 
stances to be hereafter pointed out; but its infusibility and 
inability to combine with fluxes is a very serious inconve¬ 
nience ; for after the reduction, that portion which has not 
been consumed remains disseminated with the grains of 
metal in the fused slag, and prevents the separation of all 
the metal, and the consequent formation of a good button : 
a large quantity of charcoal can thus irreparably injure an 
assay. This inconvenience does not happen, however, when 
an oxide is reduced by cementation in a lined crucible, but 
there are some cases in which its employment is inadmissible. 

Coke should never be used as a reducing agent in assays, 
when it is possible to avoid it. It often contains a very 
large proportion of earthy and other extraneous matters 
(more particularly sulphur, which is very injurious). Coke 
is never so good as wood charcoal as a reducing agent, 
because it burns more slowly. When it is used, the tempe¬ 
rature employed for an assay must be much increased. 

Coal is nearly always inconvenient, because it swells by 
heat; nevertheless, as it is not required in very large quan¬ 
tity, it is sometimes employed, being finely powdered and 
sifted previous to use. 


REDUCING AGENTS. 


157 


The Fat Oils.— The name oil is generally given to those 
bodies that are fat and unctuous to the touch, more or less 
fluid, insoluble in water, and combustible. They all become 
solid at various degrees of temperature. There are some 
which, at the temperature of our climate, have constantly a 
solid form, as butter, palm-oil, cocoanut-oil, &c. 

Tallow is an animal product analogous to the fat oils in 
properties. 

Resins. —The greater part of the resins are solid, but some 
are soft. They are brittle, with a vitreous and shining frac¬ 
ture, and are often transparent. They are very fusible, but 
cannot be raised to their boiling-point without partial de¬ 
composition. 

Although all the bodies just mentioned consume in their 
combustion a large quantity of oxygen, they cannot gene¬ 
rally effect the total reduction of an oxide on account of their 
volatility; so that, before the temperature at which the re¬ 
duction takes place can be attained, the greater part of the 
reducing agent has been expelled. They generally act only 
by virtue of the small carbonaceous residue produced by the 
action of heat; so that their use is very limited and uncer¬ 
tain. Whenever they are employed as reducing agents, with¬ 
out covering the substance, a loss is experienced, on account of 
the bubbling and boiling caused by their decomposition : this 
will always take place unless the contents of the crucible be 
covered with charcoal powder. Oils are very serviceable in 
the reduction of a large mass of oxide by cementation; in 
this case, after the oxide has been placed in the crucible, as 
much oil is added as the oxide and the lining of the crucible 
will soak up. Fat or resin is also used to prevent the oxi¬ 
dation of the surface of a metallic bath (as in the fusion of 
bar-lead samples), by coating the metal, and preventing the 
action of the atmospheric oxygen. 

Sugar in its decomposition by heat leaves a much larger 
proportion of carbon than the oils, fats, or resins; so that 
it would appear serviceable as a reducing agent. There are 
some cases in which it may be used with advantage, but it 
undergoes a great increase in volume when heated ; so that 
losses in an assay may occur by the use of this agent. To 



158 


REDUCING AGENTS. 


purify sugar from mineral ingredients, it should be recrystal¬ 
lised from alcohol. It then may be used as such, or after 
carbonisation. It yields about 14 per cent, of charcoal: 
this is pure carbon, and leaves no residue when burnt; it is, 
therefore, preferable to wood charcoal in cases where no 
foreign matter should be introduced into the assay. 

Starch, well dried, and, better still, torrefied, is employed 
with advantage as a reducing agent, and is better than 
sugar, as it neither fuses, swells up, nor spirts, and in many 
cases is even preferable to charcoal, because it is in such a 
fine state of division that it can be more readily and inti¬ 
mately mixed with the substance to be reduced. Wheat 
and rye flour have nearly the same qualities as starch. 
They are sometimes used. 

Gum decrepitates slightly by heat, softens, agglomerates, 
and boils, without spirting. The gums can be employed as 
reducing agents under the same circumstances as sugar and 

O O O 

starch, but the two latter are preferable, because they con¬ 
tain no earthy substances. 

Tartaric Acid is the reducing agent in the cream of 
tartar, or argol (KO,T,HO,T), of which so frequent use is 
made; but the acid is never employed by itself. When 
heated in close vessels, it fuses and decomposes, giving off 
combustible gases, leaving a little charcoal. It burns when 
heated in contact with air, giving rise to a peculiar and not 
unpleasant odour. 

Oxalic Acid fuses at a temperature of 208° without de¬ 
composing, but when heated to 280° it is decomposed,giving 
rise to carbonic acid, carbonic oxide, and a little formic acid 
vapour, and when heated strongly, some portions volatilise 
without decomposition; it does not leave a carbonaceous 
residue. 

The property which oxalic acid possesses of not leaving a 
residue would render it remarkably valuable for the reduc¬ 
tion of the metallic oxides in cases where the slightest trace 
of carbon is to be avoided, if its reducing power were 
greater; but it decomposes at a low temperature, and in 
burning absorbs but a small quantity of oxygen, especially 
when it lias not been dried; so that even for the most easily 


COMPARATIVE REDUCING POWERS. 


1£9 


reducible oxides a large proportion must be employed. 
When it is combined with a base, as potasli in binoxalate of 
potash, its reducing power is much augmented. 

Oxalate of Ammonia, when heated in close vessels, is de¬ 
composed. Its reducing power is nearly double that of 
oxalic acid. 

Comparative Reducing Power of the above Agents— In 


order to give an idea of the comparative reducing power 
of the agents just described, the result of some assays made 
on them by Berthier, by means of litharge, are given below. 

By heating the same weight of each reducing agent with 
an excess of litharge, buttons of lead were obtained, whose 
weights were proportional to the quantity of oxygen ab¬ 
sorbed, and by comparing them with each other the reducing 
power of each flux is given ; by taking for unity the weight 
of the reagent, calculation has proved that 1 part of pure 
carbon reduces from litharge 34*31 of lead. The following 

O O 

are the results of Berthier’s experiments :— 


Hydrogen ....... 10400 

Pure carbon ...... 34 31 

Calcined wood charcoal .... 31*81 

Amber resin ...... 30*00 

Ordinary wood charcoal .... 28*00 

Animal oil ...... 17*40 

Tallow.15*20 

llesin ....... 14*50 

Sugar ....... 14*50 

Torrefied starch . ..... 13*00 

Common starch . . . . . .11 *50 

Gum-arabic ...... 11*00 

Tartaric acid ...... 0*00 

Oxalate of ammonia ..... 1*70 

Oxalic acid ...... *90 


It must be borne in mind that these numbers do not re¬ 
present the quantities of oxygen each reagent would absorb 
in complete combustion ; but that it only indicates the 
quantity of metal produced by equal weights of the reagents. 

In assaying, however, it is rarely that these agents are 
used by themselves; they are generally mixed with a flux 
properly so called, and under the head of Fluxes they will 
be more particularly described. 

Metallic Iron removes oxygen from the oxides of lead, 
bismuth, copper, &c., but is rarely added for that especial 








1G0 


OXIDISING AGENTS. 


purpose; and when it does produce this effect, it is generally 
secondary, because it previously existed in the matter sub¬ 
jected to assay, or was added for some other purpose. 

Metallic Lead reduces but a very small number of oxides, 
but it reduces many to the minimum of oxidation; it also 
decomposes some sulphates and arseniates. 

II. OXIDISING AGENTS. 

The oxidising agents in general use are as follows :— 

1. Oxygen, atmospheric, or combined. 

2. Litharge and ceruse. 

3. Silicates and borates of lead. 

4. Nitrate of potash. 

5. Nitrate of lead. 

6. Peroxide of manganese. 

7. Oxide of copper. 

8. Peroxide of iron. 

9. The caustic alkalies. 

10. The alkaline carbonates. 

11. The sulphates of lead, copper, and iron. 

12. Sulphate of soda. 

Oxygen is a gas which has neither smell nor taste, and is 
about one-tenth heavier than atmospheric air. It has the 
property of forming compounds with nearly every element, 
and its affinities are very energetic. Atmospheric air con¬ 
sists of four-fifths nitrogen and one-fifth oxygen. 

Litharge is a fused protoxide of lead, and is generally ob¬ 
tained from the silver-lead works. When melted, it oxidises 
nearly all the metals, except mercury, silver, gold, palladium, 
platinum, &c., and generally forms very fusible compounds 
with the oxides. These two properties cause it to be a very 
valuable agent in separating silver and gold from all the 
substances with which they may be mixed. 

Litharge is occasionally mixed with a little of the red 
oxide of lead; the presence of this in large quantities becomes 
injurious, as it has the property of oxidising silver. Ordinary 
litharge can be easily freed from this oxide by fusing it and 


ACTION OF OXIDE OF LEAD. 


161 


pouring it into a cold ingot mould, then pulverising, and 
carefully keeping it from contact with air, as it readily absorbs 
oxygen, and if it be allowed to cool in the atmosphere, it 
will nearly all be converted into the red oxide. 

Ceruse, or White Lead, is a carbonate of the protoxide of 
lead. As it does not contain the slightest traces of red oxide, 
it may be used where the presence of that substance may be 
inconvenient; but it is troublesome to use, as it is much less 
dense than litharge ; large vessels must be employed in con¬ 
sequence ; besides, it generally contains a small quantity of 
acetate or subacetate of lead, and sometimes metallic lead 
separates from it on ignition, which is, in some cases, disas¬ 
trous to the result of an experiment. When ceruse is em¬ 
ployed, a certain quantity must be fused, to ascertain if any 
metallic lead be produced; * and, on the other hand, it 
must be examined to ascertain if it be adulterated with sul¬ 
phate of baryta. When it is pure, it dissolves completely 
in acetic or nitric acid. 

Action of Oxide of Lead on the Metals. —The following 
are the results of the experiments of Berthier on the action 
exercised by oxide of lead on sulphur, selenium, tellurium, 
arsenic, and the most common of the metals. The experi¬ 
ments were made in a furnace capable of producing heat 
enough for a copper assay. 

Sulphur. —Oxide of lead is completely reduced by sul¬ 
phur, with the formation of sulphurous acid, but not a trace 
of sulphuric acid : thus S + 2PbO = 2Pb + S0 2 . 

Selenium is dissolved by oxide of lead in all proportions; 
but these bodies exercise no action on each other. 

Tellurium is strongly attacked and converted into telluric 
acid, which combines with the oxide of lead when the latter 
is in excess (Te + 4PbO = 3Pb + Pb0,Te0 3 ). If the contrary 
be the case, the excess of acid is volatilised and telluride of 
lead produced (2Te + 3Pb0 = Te3Pb + Te0 3 ). 

Arsenic. —When metallic arsenic is heated with litharge, 
if the latter be employed in great excess, all the arsenic is 
oxidised (As +3PbO = As0 3 +3Pb); if not, a part only is 


* Berthier. 
M 


162 


ACTION OF OXIDE OF LEAD 


oxidised, and lead reduced; the remainder volatilises, or 
forms an arsenide of lead. (For nature of reaction, refer to 
the preceding metal, Tellurium). Mixtures of: 

Arsenic . . . 75*24 3700 0-40 

Litharge . . .111*00 111*60 111*00 

gave : No. 1, a lamellar metallic button, and a compact 
vitreous slag of a fine orange-colour. The fusion was 
accompanied by a considerable amount of arsenical 
smoke. 

No. 2 gave a semiductile metallic button, with a lamellar 
fracture, like galena, but not so blue, and a transparent vi¬ 
treous orange-coloured slag. 

The third yielded a button of lead and a deep olive-green 
slag, very crystalline, and in large plates. This fusion was 
not accompanied by smoke. It is probable that arsenious 
acid is formed in these reactions : the last slag contained 
about a fifth of its weight of this acid. 

Lead reduces, in part, arsenious acid ; in the same manner, 
arsenic partly reduces oxide of lead. A mixture of 

Arsenious acid . . . . . .12*40 

Lead.38*80 

produced on fusion a very arsenical vapour, and yielded 
32 parts of arsenide of lead, which was deep grey, semi- 
ductile, and had a granular fracture ; a fine orange-yellow 
vitreous arsenite of lead was also produced. 

Antimony. —The two following mixtures of antimony and 
litharge : 

Antimony.10 10 

Litharge. 40 80 

gave (No. 1), 23 parts of lead, and a compact well-fused 
slag, of a topaz yellow colour, which contained more than 
one-third of its weight of protoxide of antimony (Sb-f 
SPb0 = Sb0 3 +3Pb). The second gave 26 parts of lead, 
and a very fluid glass, which cooled rapidly, and was opaque, 
like yellow wax ; it contained : 

Oxide of lead . . . , ,52 

Protoxide of antimony . . . .11*86 


UPON VARIOUS METALS. 


163 


Tin. —This metal, cut into small fragments, was heated 
with the following quantities of litharge: 

Tin .... 10 10 10 

Litharge . . . 37'5 80 120 

The first mixture gave a slaggy substance, of dull grey 
colour, not well fused, with globules of lead at the lower 
part. 

The second mixture gave 26 parts of lead, and a semi- 
iused slag, compact and opaque, the colour yellowish-grey. 
It contained : 

Oxide of lead.52 

Protoxide of tin ...... 11’4 

The third mixture produced 26‘3 of lead, and a very 
fluid slag, which was compact, opaque, and greyish yellow, 
with a granular fracture (Sn + PbO = SnO + Pb). It con¬ 
tained : 

Oxide of lead.97-0 

Oxide of tin ..11*4 

Zinc. —Ten parts of zinc filings and 100 of litharge were 
heated together; as soon as the latter softened, action 
commenced. A slight bubbling and flaming, occasioned 
by the combustion of a portion of the zinc, took place, 
and on increasing the heat the mixture fused completely. 
The result was a button of lead equal to 13 parts; 
it was pure and ductile, and was covered with a crystal¬ 
line slag, like litharge, opaque and yellowish, but in 
small plates. This experiment proves that about one- 
fifth of the zinc employed is volatilised, whilst the re¬ 
mainder reduces the litharge (Zn + PbO = ZnO + Pb). The 
slag contains: 

Oxide of lead ..877 

Oxide of zinc ...... 123 

Bismuth. —Twenty parts of bismuth heated with 40 of 
litharge, gave a ductile metallic button, tin-white, and 
weighing 24*3 parts, and a crystalline slag, like litharge. 

M 2 



164 


ACTION OF OXIDE OF LEAD. 


Iron. —M. Berthier heated metallic iron with litharge in 
the following proportions : 

Iron wire .... 10 10 

Litharge .... 100 160 

The first mixture gave 40 of lead, and a pasty, compact, 
opaque slag, of a deep metallic black-colour, and very 
magnetic (Fe + PbO = FeO +Pb). There was no metallic 
iron, but some globules of lead were present. The slag con¬ 
tained about: 

Oxide of lead . . . . . .55-9 

Oxide of iron . . . . . . 13 4 


The second mixture gave a button of lead, weighing 46*6, 
and a very fluid, compact, opaque slag, with an unequal 
shining lustre, deep-brown, and very magnetic. The slag 
contained, nearly : 

Oxide of lead . . . . . <110 

Oxide of iron ...... 13*4 

Copper. —The following are the results obtained with dif¬ 
ferent mixtures : 

Copper 15-8 15-8 15 8 15 8 15-8 

Litharge 13*9 279 55*8 167*4 334*8 


With the first mixture a button was produced, copper- 
red on the exterior, grey in the interior, weighing 17 parts; 
and a compact, opaque, deep-red slag. The slag contained: 

Oxide of lead ...... 10*3 

Saboxide of copper.2*4 

and the button : 


Copper . 
Lead 


. 13*6 
. 3*4 


The button produced by the second mixture was ex¬ 
teriorly copper-red, and interiorly grey, spotted with red; 
it weighed 17-8, and the slag was compact, reddish-brown, 
and opaque. The slag contained: 

Oxide of lead.22*3 

Suboxide of copper ..... 3*6 

and the button : 


Copper . 
Lead 


. 12*4 
. 5*2 



ACTION OF OXIDES OF COPPER. 


165 


The third mixture gave a button similar to the last, 
weighing 18 parts, and a compact, opaque, reddish-brown 
slag. It contained : 


Oxide of lead 
Suboxide of copper 

The button was composed of: 

Copper .... 
Lead .... 


. 49-8 
. 3-8 


. 12-4 
. 5-6 


With the fourth mixture, a button weighing 25-6 was 
produced, and a slightly crystalline, reddish-brown slag, 
which contained: 


Oxide oflead.151-28 

Suboxide of copper ..... 10-32 

and with the fifth, a grey metallic button, weighing 23-6, 
and a crystalline slag in large plates, like litharge, yellow¬ 
ish-green and reflecting green. The analysis of the button 
gave: 

Copper.3 G 

Lead.200 

and the slag contained: 

Oxide of lead ...... 313-28 

Suboxide of copper.13-72 

Action of the Oxides of Copper upon Lead. —The oxide is 
speedily reduced to the state of suboxide by excess of lead. 
If the lead be not in excess, it is totally oxidised, reducing 
a corresponding quantity of the copper to the minimum of 
oxidation. 

• The oxide is reduced to the metallic state by lead, but 
not completely, because a certain quantity is taken up by 
litharge. The following mixtures have been made the sub- 
ject of experiment: 

Metallic lead . . 25-9 25-9 25 9 38-8 51-8 

Suboxide of copper .19-8 14 9 9 9 9-9 9*9 

All of these gave an imperfect alloy of copper or lead, and 
a very fusible slag composed of oxide of lead and suboxide 
of copper. The first produced a very small globule of 



1G6 


OXIDISING FLUXES. 


copper and a very fluid slag, having a much greater tendency 
to run through the body of a crucible than litharge. Cooled 
slowly, it was reddish-brown, opaque, and had a finer 
texture. It was composed of: 

Oxide of lead ...... 27 9 

Suboxide of copper ..... 17*8 

The second mixture produced a button ot copper weigh¬ 
ing 4'4, and a deep reddish-brown slag, composed ot: 


Oxide of lead 

. 27-7 

Suboxide of copper 

. 8-7 

The button gave : 


Copper. 

. 4-1 

Lead ..... 

. . . 03 

The third gave a metallic button 

weighing 8*8, and a dee}) 

red, opaque slag, which contained : 


Oxide of lead 

. 24-89 

Suboxide of copper 

. 211 

The button contained : 


Copper ..... 

. 59 

Lead ..... 

. 2-9 


In the fourth and fifth mixtures, buttons weighing 21'2 
and 34*8 were produced, together with slags similar to the 
preceding, and containing about 8 per cent, of suboxide of 
copper. 

Silicates and Borates of Lead behave as litharge, but they 
oxidise less rapidly. 

They may be prepared by fusing together 1 part of silica 
or boracic acid with 1 part of litharge. The borates are 
more fusible than the silicates, but their use is attended 
with an inconvenience ; they swell very much in fusing. 

Nitrates of Potash and Soda fuse at a temperature below 
redness, without alteration, but when heated more strongly, 
they give up oxygen. The action of these salts, when fused, 
is very energetic, because they have a great tendency to 
decompose, and because they contain a large quantity of 
ox} 7 gen. They are used as oxidising agents in the purifica¬ 
tion of the noble metals, and for preparing some fluxes. 
They ought always to be employed in a state of purity. 


IMPURITIES IN SALTPETRE. 


1G7 


Saltpetre often contains impurities. On this account a 
determination of the real amount of nitrate of potash often 
becomes necessary, not only in cases where saltpetre is to be 
used for docimetric purposes, but also when used in certain 
technical operations, viz. the manufacture of gunpowder, 
enamel, &c. 

It saltpetre is very impure, it may be purified by re- 
crystallisation to such a degree, that it will only contain 
2 to 3 per cent, foreign substances (chiefly chloride of 
sodium). 

An exact assay of saltpetre is most difficult, and the 
different modes in use are not quite exact, on account of the 
chemical properties of the nitric acid, potash, and soda, 
which substances are generally contained together in 
saltpetre, and cannot be perfectly estimated by means of 
reagents. This is chiefly the case v T ith the nitric acid and 
soda. 

Soda is frequently found in saltpetre, as the manufacturers 
often intentionally mix the raw saltpetre with soda-saltpetre, 
and it is also often manufactured from a mixture of soda- 
saltpetre and carbonate of potash. 

The following are the different modes of assaying salt¬ 
petre. 

a . Huss’s Mode.— This is the most simple mode, and used 
with success in several parts of Germany. 

It is based upon the fact, that the saturation of a certain 
quantity of water with saltpetre depends on the tempera¬ 
ture of the water, and also that a solution of impure salt¬ 
petre in hot water crystallises on cooling, the sooner, the 
more free it is from foreign salts. Huss has determined 
this degree of saturation for a certain quantity of water at 
different temperatures, viz. from 8—20£° R., raising by ^°, 
and has averaged the results in a table which shows 
the percentage of pure saltpetre contained in raw salt¬ 
petre. 

Forty parts of dried saltpetre are dissolved in 100 parts of 
pure water of 45—50° R. This is done in a tared glass 
beaker, which is covered with a glass plate, in order to 
avoid loss of water by evaporation. The glass plate is 


168 


ASSAY OF SALTPETRE. 

furnished with a hole for receiving the thermometer. The 
water is then stirred till all the saltpetre is dissolved. If 
during solution insoluble substances (partly of organic origin) 
are separated, the liquid is to be filtered. The thermo¬ 
meter, divided into £ degrees, is put into the solution, 
and the liquid is stirred all the time, so that the temperature 
of it is throughout alike; for the same reason the beaker 
is also put upon thick layers of paper which rest upon wood. 
The moment the saltpetre begins to crystallise is then 
to be observed, and, at the same time, the degree of tem¬ 
perature which the solution possesses at that moment. The 
following table will show the amount of saltpetre contained 
in solution. 


If a solution of com¬ 
mon saltpetre begins 
t > crystallise at the 
following degrees of 
Reaumur’s ther¬ 
mometer 

100 parts of the assayed 
saltpetre contain the 
following parts by 
weight of pure nitrate 
of potash. 

If a solution of com¬ 
mon saltpetre begins 
to crystallise at the 
following degrees of 
Reaumur’s ther¬ 
mometer 

100 parts of the assayed 
saltpetre contain the 
following parts by 
weight of pure nitrate 
of potash. 

8° 

55-7 

14*° 

75 

H 

56-3 

14* 

75-9 

8* 

57 

14* 

76-8 

8* 

57-7 

15 

77-7 

9 

58-4 

15* 

78 6 

0* 

591 

15* 

79-6 

9* 

59-8 

15| 

80 5 

»* 

00-5 

16 

81-5 

10 

61 3 

16i 

82-4 

10* 

62 

16 

83-4 

10* 

62-8 

16? 

84-4 

lot 

63-5 

17 

85-4 

11 

64-3 

17* 

86-4 

Hi 

65 

17* 

87*4 

1H 

65-8 

17* 

88-4 


66-6 

18 

89-5 

12 

67-4 

Wi 

90-6 

12* 

68-2 

18* 

9]-7 

12* 

69 

18| 

92-9 

12* 

69 8 

19 

94 

13 

70 7 

19* 

95-2 

m 

71-5 

19* 

96-4 

13* 

72-4 

id* 

97-6 

13? 

73*2 

20 

98-8 

14 

741 

20? 

100 


In case a solution does not crystallise at the temperature 
of 8°, it may be considered as proof that the saltpetre is 
very impure. In order to determine the amount, it is 
mixed with an equal part of perfectly pure saltpetre.’ This 

































169 


ASSAY OF SALTPETRE. 

mixture is dissolved and determined as before, and the 
pure saltpetre added is then deducted from the result. 

For performing this assay, it is necessary to pulverise the 
saltpetre as finely as possible, in order to dissolve it quickly. 
It is also necessary not to use too small quantities. 2^ oz. 
saltpetre, and 6^ oz. water, are suitable quantities. The 
temperature of the water must not exceed 50—55°, other¬ 
wise the amount of saltpetre will appear too high (owing to 
water having been evaporated), and the same error will 
be produced if the solution is not properly stirred. The 
best thermometers for this purpose are those filled with 
alcohol, as the latter expands by heat 8 times more than 
mercury, and thus a more exact observation of the frac¬ 
tions of the degrees is obtained. When using Huss’s table, 
it is necessary that the thermometers employed should 
exactly correspond with Huss’s thermometer; if this is not 
the case, the difference between the two thermometers is to 
be ascertained by trials with solution of pure saltpetre. 

b. Gay-Lussac’s mode of assaying saltpetre consists in 
converting the nitrate of potash into carbonate of potash, 
and in determining its amount volumetrically by means of 
standard sulphuric acid. 2'639 grs. saltpetre are mixed 
with 1 gr. of ignited pine-root, and 12 grs. ignited and finely- 
pulverised chloride of sodium (the latter is added in order 
to moderate the combustion), and this mixture is heated in 
a platinum crucible. After cooling, the mass is extracted 
by water, and either standard solution of sulphuric acid or 
oxalic acid is added to the solution. The sulphuric acid is 
prepared by mixing TO grs. English sulphuric acid with 
600 grs. water, and to this mixture so much water is added 
again that 100 measures of it will saturate 6,487 grs. car¬ 
bonate of potash. • The number of measures used for satu¬ 
ration will then indicate directly the percentage of carbonate 
of potash. 

The following foreign substances in raw saltpetre should 
be determined. 

Water .—Twelve to 20 grammes of air dried, finely-pul¬ 
verised saltpetre, are heated in a porcelain crucible to 120°C., 
and the resulting loss is calculated as water. 




170 


ASSAY OF SALTPETRE. 

Mechanically-mixed Impurities. —The substance obtained 
in the former assay is dissolved in hot water, and filtered 
through a dried and weighed filter. The residue is well 
washed with hot water, dried on the filter at 120° C. and 
weighed. On deducting the weight of the filter, there will 
be left the weight of the mechanically-mixed impurities 
(alumina, silica, carbonate of lime, peroxide of iron, &c.), 
which usually amount to 2 to 5 per cent. 

Lime and Magnesia. —These substances are precipitated 
as carbonates in the former filtered solution, raised to the 
boiling-point, by carbonate of soda; the carbonates are 
then dissolved in hydrochloric acid, and neutralised with 
ammonia. The lime can be precipitated by oxalic acid, and 
filtered off; the magnesia which remains in solution may 
then be precipitated by phosphate of soda. 

The amount of lime in East Indian raw saltpetre which 
has been once crystallised, varies between 0-216 and 0-265 
per cent., the amount of magnesia between 0-263 and 0-28 
per cent. 

Chlorine. —Two to 3 grammes of raw saltpetre are dissolved 
in about 30 grammes pure warm water, in a flask furnished 
with a tight fitting stopper, and the amount of chlorine is 
determined by a standard solution of nitrate of silver. The 
latter is prepared by dissolving 4*793 grammes of nitrate of 
silver in 1000 burette divisions of water, each division of 
the burette will then indicate 0-001 gramme of chlorine. 
The solution, after being warmed and acidulated with nitric 
acid, s mixed gradually with the solution of silver; after 
each addition of the latter, it is to be shaken and then allowed 
to rest. 

The amount of chlorine determined by this assay is calcu¬ 
lated as being derived from § chloride of potassium, and 
i chloride of sodium, so that 1 part of chlorine corresponds 
to 1-927 part of metal (1-285 potassium, 0-642 sodium. 
Experience has proved that East Indian saltpetre contains 
chloride of potassium and sodium in these proportions. 

Sulphuric Acici —Six to 8 grammes of raw saltpetre are 
dissolved, and from this solution diluted, and heated to the 
boiling-point, the sulphuric acid is precipitated by means 


ASSAY OF SALTPETRE. 


171 


of a standard solution of baryta. By using a solution of 
3*26 grammes nitrate of baryta in 2000 parts of the burette, 
each division of the latter will correspond to 0*0005 gramme 
sulphuric acid. The amount of sulphuric acid in East 
Indian raw saltpetre varies between 0 05 and 0*11 per 
cent. 

Nitrate of Socla .—This determination is most difficult, 
and the following modes are recommended. 

a. Perfectly pure potash-saltpetre is mixed with different 
quantities of soda-saltpetre. These mixtures are put under 
a glass bell jar, together with a quantity of the raw-saltpetre 
to be assayed. The glass bell must contain also a vessel 
with water. After a certain time, it is ascertained which 
of the standard samples corresponds in weight with the 
raw saltpetre. 

The results so obtained are of value only if no other 
hygroscopic salts (chloride of magnesium, &c.) are present. 

0 . Longchamps’ mode is based upon the decomposition 
of soda-saltpetres by chloride of potassium, producing 
chloride of sodium and nitrate of potassium. The saltpetre 
is mixed with chloride of potassium, and the solution eva¬ 
porated down. By this operation, chloride of sodium 
becomes first separated, and afterwards saltpetre. The 
latter is washed, dried at 150° C., and weighed. Werther 
has recommended a similar mode. 

7 . According to Bagsky, the flame of alcohol takes a 
yellow tinge when mixed with saltpetre containing soda. 

If the saltpetre does not contain certain oxides, such as 
alumina, lime, &c. (or if, previously present, they have been 
precipitated), a solution of antimoniate of potash will preci¬ 
pitate the soda contained in saltpetre solution. The preci¬ 
pitate consists of antimoniate of soda, 100 parts of which 
contain 84*39 antimonious acid, and 15*61 soda. 

The presence of soda is also to be ascertained by washing 
saltpetre with a saturated solution of pure potash-saltpetre. 
This saturated solution will then contain a proportionally 
large amount of nitrate of soda. If a small quantity of the 
solution is made to crystallise upon a watch glass, soda- 
saltpetre, showing a rhombohedric form, may be detected 



172 


ASSAY OF GUNPOWDER. 


by means of a microscope, while potash-saltpetre crystallises 
in prisms, and chlorides of sodium and potassium in cubes 
arranged in the form of steps. 

Soda-saltpetre ( Chili- or cubic-saltpetre ), may, in many 
cases, be substituted for potash-saltpetre. 

[It may be here appropriate to give the method of as¬ 
saying gunpowder. 

a. The water is ascertained by drying a suitable quantity 
of gunpowder, at 100° C. in an air or water-bath. Two 
trials must give equal weights. 

b. To determine the saltpetre , the same quantity of gun¬ 
powder is moistened with water, finely pulverised, put upon 
a filter, and washed out completely with hot water. The 
filtered solution is evaporated to dryness in a small tared 
porcelain vessel, the mass dried at about 200°C., and weighed 
as saltpetre. 

c. To ascertain the amount of sulphur , a mixture of 3 grs. 
gunpowder, 3 grs. carbonate of soda, and 15 grs. chloride of 
sodium (to moderate the combustion),are heated in a crucible. 
The resulting mass contains sulphates. After cooling, 
it is dissolved in water, saturated with nitric acid, and 
precipitated by chloride of barium. The solution is then 
warmed and allowed to settle again, the pure solution is 
poured upon a filter, and the precipitate is stirred up with 
hot water, and allowed to settle down again. This operation 
is repeated several times, in order to prevent a portion of 
the precipitate going through the filter. After having 
washed it completely, the sulphate of baryta is dried upon 
the filter, then burned and weighed. 100 parts sulphate of 
baryta contain 13*71 sulphur. 

d. The amount of carbon is represented by the difference. 
The quality of it may be ascertained if the residue from 
solution b is boiled with a solution of KS (without free KO). 
The sulphur will be extracted, and the carbon will remain 
as a residue; it may then be washed and dried. 

The quality of gunpowder may be judged roughly from 
the amount of saltpetre contained in it. To determine that 
amount quickly, a hydrometer may be used which indi- 


173 


OXIDISING FLUXES. 

cates the percentage of saltpetre, if a certain quantity of 
powder is lixiviated with a certain quantity of water. The 
hydrometers used in Austria are arranged for 400 grammes 
powder, 1 lb. water, and for a temperature of IT'4° C. The 
results are exact within \ per cent. 

To estimate the strength of the powder, it is necessary to 
take into consideration its exterior properties, viz. com¬ 
pactness, size and form of grains, &c.] 

Nitrate of Lead acts in a similar way to the two last 
mentioned salts. It is prepared by dissolving litharge in 
nitric acid, and crystallising the solution. 

Peroxide of Manganese is easily reduced to the state of 
protoxide by many metals, and is a very powerful oxidising 
agent; but is rarely employed, because its compounds are 
very infusible. It is employed occasionally in the purifica¬ 
tion of gold and silver. 

Oxide of Copper is not much employed as a flux, but is often 
contained in substances submitted to assay; it then acts as 
an oxidising agent. A great number of metals, even silver, 
reduce it to the minimum of oxidation : and other metals, as 
iron, for instance, totally reduce it. 

Peroxide of Iron.— This, like oxide of copper, sometimes 
acts accidentally as an oxidising agent. 

The Caustic Alkalies, Potash and Soda, fuse below a 
red heat, and volatilise sensibly at a higher temperature. 
Charcoal, at a high temperature, decomposes the water com¬ 
bined with the hydrates of potash and soda, converting them 
into carbonates, but an excess at a white heat decomposes 
the carbonate, and potassium or sodium is the product. 

Carbonates of Potash and Soda are very much employed 
as agents in the assay by the dry way. They have the 
power of oxidising many metals, as iron, zinc, and tin, by 
the action of the carbonic acid they contain ; part of it being 
decomposed, with the formation of carbonic oxide. 

Sulphates of Lead, Copper, and Iron. —These three salts 
at a high temperature oxidise the greater number of the 
metals, even silver, the sulphuric acid giving off oxygen and 
sulphurous acid. They are used in the assay of gold. 



174 


DESULPIIU RISING REAG ENTS. 


Sulphate of Soda is not used by itself as a reagent, but 
is a product in many operations : it is either formed in the 
course of an assay, or is contained as an impurity in some 
of the bodies used. 

III. DESULPHURISING REAGENTS. 

1. The oxygen of the atmosphere. 

2. Charcoal. 

3. Metallic iron. 

4. Litharge. 

o 

5. The caustic alkalies. 

6 . The alkaline carbonates. 

7. Nitre. 

8 . Nitrate of lead. 

0 . Sidphate of lead. 

1. The Oxygen of the Atmosphere acts as a desulphurising 
agent in roasting, combining with the sulphur present, form¬ 
ing sulphurous acid (2FeS 2 + 110=Fe 2 0 3 + 4S0 2 ) or sulphuric 
acid (CuS +40 = Cu0,S0 3 ), sometimes both. 

2. Charcoal decomposes many sulphides by taking their 
sulphur to form sulphide of carbon. It acts in this man¬ 
ner with the sulphides of mercury, antimony, and zinc 
(2ZnS-K C = 2Zn + CS 2 ). It is only employed as an auxi¬ 
liary to the desulphurising power of the alkalies and their 
carbonates. 

3. Iron separates sulphur from lead (PbS + Fe = Pb -f FeS), 
silver, mercury, bismuth, zinc, antimony, and tin, but only 
partially decomposes the sulphide of copper. It is generally 
used in the state of filings, or nails; the latter are prefer¬ 
able, and ought to be kept free from rust. Oxide of iron 
may be used if it be mixed with the requisite quantity of 
charcoal to reduce it. Cast iron must not be employed, as 
it has very little affinity for sulphur. 

4. Litharge (PbO) exercises a very energetic action on 
sulphides, even at a low temperature. If it be employed in 
sufficient proportion, the sulphide acted on is wholly decom¬ 
posed. The sulphur is often disengaged as sulphurous acid, 


LITHARGE. 


175 


and the metal remains alloyed with the lead proceeding 
from the reduction of a portion of the litharge, or combines 
as oxide with that portion of the litharge which is not 
reduced. The quantity of litharge requisite for the decom¬ 
position of a sulphide is considerable, and varies according 
to its nature ; some sulphides require 34 times their weight. 
When less than the requisite quantity is used, only a portion 
of the sulphide is decomposed, and a corresponding quantity 
only of lead reduced, whilst the remainder of the sulphide 
forms, with the litharge and the metallic oxide which can be 
produced, a compound belonging to the class of oxysulphides, 
which is generally very fusible. 

When the sulphides have a very strong base, as an alkali 
or alkaline earth, no sulphurous acid is given off by the 
action of litharge, but all the sulphur is converted into sul¬ 
phuric acid. 

Litharge is a very valuable reagent, and its use is nearly 
exclusively confined to the assay of sulphides containing the 
noble metals, as these metals are thus obtained as alloys of 
lead, which are afterwards assayed by cupellation. 

The following is an account of the behaviour of this 

o 

reagent with the ordinary sulphides. 

Sulphide of Manganese requires at least six times its 
weight of litharge to produce a fusible compound, and 
thirty times its weight to desulphurise it completely. The 
sulphur and metal oxidise simultaneously (MnS + 3PbO = 
MnO-f S0 2 +3Pb), and a protoxide of manganese is formed, 
which partly peroxidises, taking a brownish tint in contact 
with the atmosphere. Berthier assayed the four following 
mixtures : 

Sulphide of manganese .5 5 5 5 

Litharge . . . .20 30 100 150 

The first produced an infusible, greyish-black, scoriform 
mass, in which small plates, having the look of galena, could 
be discovered. It was composed of the sulphides and oxides 
of manganese and lead. Much sulphurous acid was given off 
during the operation. 

The second fused to a soft paste, and gave 17*5 of lead, 
and a compact, vitreous, opaque slag, of a very deep brown 


17G 


LITHARGE. 


colour. The slag contained about half its weight of sulphide 


of manganese. 


The third fused readily, and produced 31'5 of ductile 
lead, and a transparent, vitreous sing, of a deep hyacinth 


red. 

The fourth produced 33*7 of lead, exceedingly ductile, 
and the desulpliurisation was complete. 

Sulphide of Iron .—Thirty parts of litharge are suffi¬ 
cient to scorify protosulphide of iron ; the metal is con¬ 
verted into the protoxide (FeS + 3PbO = FeO + S0 2 + 3Pb). 

The four following mixtures: 


Protosulpliide of iron . .10 10 10 10 

Litharge . . . . .00 125 250 300 


gave, the first a pasty, scoriform mass, colour metallic 
grey, and very magnetic. It was composed of the sulphides 
and protoxides of iron and lead. 

The second gave a very fluid metallic black slag, very 
magnetic, opaque, and possessing great lustre, and 3G of 
lead. 

The third gave a compact vitreous transparent slag of a 
fine resin-red, and 67 of lead. 

The last yielded a similar slag to the former, but 
containing no sulphur, and 70 of lead. 

Native iron pyrites w r as treated with the following pro¬ 
portions of litharge: 

Iron pyrites . .10 10 10 10 10 10 

Litharge . . . 00 125 200 300 400 500 


The mixtures fused very readily with an abundant disen¬ 
gagement of sulphurous acid. 

The first produced only a metallic button, divisible into 
two parts: the lower was the largest, and was a subsul¬ 
phide of lead ; the other looked like the compact galena, 
but was magnetic ; it was composed essentially of the sul¬ 
phides of iron and lead, but probably contained a small 
quantity of their oxides. 

The second and third gave black vitreous opaque slags 
which stained the crucibles brown, together with lead, 
having a granular fracture, and a deep grey colour : the 
first button weighed 35, and the second 40. Both samples 


ACTION OF LITHARGE ON SULPHIDES. 


177 


of lead were contaminated with a small quantity of slag, 
and contained from T -^ 0 - 0 -ths to T J- 0 tli of sulphur, and a 
small quantity of iron. 

The slags from the three last mixtures were vitreous, 
transparent, and of a fine resin-red ^colour: the buttons of 
lead weighed 45*4, 54*8, and 86 parts. A much larger 
proportion of litharge does not produce more than 86 of 
lead, proving that 50 parts of litharge completely effect the 
desulphurisation of iron pyrites. 

Sulphide of Copper .—The following mixtures of sulphide 
of copper and litharge 

Sulphide of copper. .10 10 10 10 10 

Litharge ... 20 30 50 100 250 

fuse very readily, giving off an abundance of sulphurous 
acid. 

The slags formed were compact, vitreous, opaque, or 
translucid, and more or less bright red. The copper which 
they contained was at the minimum of oxidation. 

The three first mixtures gave metallic buttons, composed 
of uncombined lead and sulphide of copper. 

The fourth gave 28 of lead, with a little adhering sulphide 
of copper. 

The fifth gave 38-5 of pure ductile lead, the exact quan¬ 
tity that ought to be reduced from litharge by the transfor¬ 
mation of the above quantity of sulphide of copper into 
suboxide and sulphurous acid (2CuS + 5Pb0 = Cu 2 0 + 2S0 2 + 
5I*b). _ . 

Sulphide of copper does not combine with litharge ; this 
is an exception to the general rule. It requires about 
twenty-five times its weight of litharge to decompose it 
completely. When litharge is combined with a certain 
quantity of protoxide of copper, it has no action on the 
sulphide of that metal. 

The desulphurisation of copper pyrites requires about 30 
parts of litharge. 

Copper pyrites .... 10 10 10 10 

Litharge. 50 100 200 3C0 

were fused together. 

In the first assay the fusion was accompanied with much 


178 


ACTION OF LITHARGE ON SULPHIDES. 


ebullition, and the mass remained pasty : G parts of ductile 
lead were produced, and a matte similar to galena, but 
deep grey, with small facets, and a brownish-black vitreous 
slag. 

In the second, muoh ebullition and swelling up took 
place: 35 of lead, 45 of matte, and a dec]) brown vitreous 
slag, were produced. 

In the third assay, 49 of lead was the result. It was 
covered by a thin layer of matte, and a very shining, deep 
brown, vitreous, translucid slag. 

The last mixture fused readily, almost without ebullition, 
and gave 72 of lead, and a compact shining slag, of a bright 
grey, and without the least trace of matte ; the desulphuri- 
sation was complete (CuS,FeS-f 6PbO = CuO + FeO + 2S0 2 ). 

Sulphide of Antimony has a great tendency to combine 

with litharge, and it must be heated with at least 25 parts 

to effect its desulphurisation. By mixing these two substances 

in the following proportion : 

Sulphuret of antimony . 10 10 10 10 10 

Litharge . . .38 60 100 140 250 

the three first mixtures afforded very fluid slags, compact, 
deep black, and slightly metallic, and buttons of ductile 
lead, weighing 2, 9, and 2G parts. These slags resemble 
the black litharge produced at the commencement of a 
cupellation. 

The fourth mixture gave a transparent compact slag, 
vitreous and shining, having a splendid hyacinth-red colour, 
and 50 parts of lead. 

The last produced 57 of lead, proving the desulphurisation 
to be complete (SbS 3 + 9Pb0 = Sb0 3 + 3S0 2 + 9Pb). The 
antimony, in this case, exists as protoxide in the slag. 

M. Fournet has observed that sulphide of antimony has 
the property of carrying sulphide of copper, and even sul¬ 
phide of silver, into the compounds formed with litharge. 
In one of the experiments which he made, a double sulphide, 
composed of equal parts of sulphide of silver and sulphide of 
antimony, was fused with three times its weight of litharge, 
and gave, firstly, a button of lead, mixed with silver; 
secondly, a matte like galena; and thirdly, a black slag. 


ACTION OF LITHARGE ON SULPHIDES. 


179 


This slag was analysed, and found to contain from 8 to 9 
per cent, of silver. 

It is probable that all the sulphides having a strong ten¬ 
dency to combine with oxide of lead, have, like sulphide of 
antimony, the property of determining the scorification of a 
certain quantity of sulphide of silver; like all the sulphides, 
which in a state of purity, are completely decomposed by 
oxide of lead. 

Sulphide of Zinc must be fused with twenty-five times its 
weight of litharge to be decomposed. The following mix¬ 
tures were heated together: 

o 

Blende .... 2408 12-08 10 10 
Litharge .... 55-78 83-G8 100 250 

However strongly the first mixture was heated, it always 
remained pasty; 29’2 of a greyish-black lead were pro¬ 
duced, which contained -018 of sulphur and *008 of zinc. 
The button was covered by a metallic-looking black sub¬ 
stance, intermediate between a matte and a slag: it was 
composed of the sulphides and oxides of zinc and lead. 

The second mixture gave 35 5 of lead and a fluid slag, 
which was compact, opaque, and black. 

The third gave 43 of lead, and a deep grey slag. 

The last produced 65 of pure lead (ZnS+.3PbO ZnO 
+ S0 2 + 3Pb), and a vitreous slag, of an olive-colour, and 
translucid on the edges. 

Sulphide of Lead .—Galena and litharge, at a heat just suffi¬ 
cient to fuse them, combine and form an oxysulphide; but 
if the temperature be increased, the two bodies react on 
each other, and are mutually decomposed (PbS -f 2PbO = 3Pb 
-f S0 2 ). If 2789 parts of litharge be employed to 1496 of 
lead, or 1865 of litharge to 1000 of galena, nothing but pure 
lead is obtained. If more litharge be employed, a portion 
is not decomposed, and covers the lead. If less be employed, 
the galena is not completely decomposed, and the lead is 
covered by a matte of subsulphide. 

But when litharge is combined with a certain proportion 
of sulphides or metallic oxides, it completely loses its oxi¬ 
dising power on galena, even at a white heat ; so that it can 

N 2 



180 


CAUSTIC ALKALIES AND CAKBONATES. 


be combined with this substance as with the other sulphides, 
without effecting its total decomposition. 

5, 6. Caustic Alkalies and their Carbonates. —All the 
sulphides are decomposed by caustic alkalies, and their car¬ 
bonates ; but in the latter case carbonaceous matter must be 
present. In the absence of charcoal, there are some sul¬ 
phides, as of copper, on which they have no action. In these 
decompositions alkaline sulphides are formed, and combine 
with and retain a certain quantity of the sulphide submitted 
to experiment. The proportion of the sulphide which re¬ 
mains in combination with the alkaline sulphides depends on 
many circumstances. It is always less when a large propor¬ 
tion of alkali or carbonate has been employed ; as it is also 
when a high degree of temperature has been employed ; and 
the presence of charcoal always much diminishes the pro¬ 
portion. When the metal of a sulphide is very volatile, as 
mercury or zinc, the decomposition may be perfect. 

Potash, as it is sold in commerce, always contains foreign 
substances, viz. silica, peroxide of iron, sulphate, muriate, 
phosphate and silicate of potash, soda-salts, etc. and also 
water. 

A partial purification of the potash may be effected by 
dissolving it in boiling water, which will not dissolve some 
of the above named foreign substances. 

The amount of carbonate of potash contained in potash, 
may be ascertained by standard solution of oxalic acid, or 
by tartaric acid. Mohr * recommends for this purpose the 
use of oxalic acid. 

Soda also is never free from foreign substances. 

The determination of carbonate of soda may be effected 
also by tartaric acid, or by a salt of oxalic acid. 

When employing a standard solution, sulphuric acid is 
taken, sometimes oxalic acid, while for the determination of 
potash, a standard solution of oxalic acid is always used. 

Carbonate of ammonia is used for decomposing metallic 
sulphates which are formed during the roasting process of 
several sulphur minerals. Sulphate of ammonia is then 
formed, which is volatile when slightly heated. 

* Mohr, Lulirb. cl. Titriennetliode, 1855. 


NITRATE OF POTASII. 


181 


7. Nitre, Saltpetre, or Nitrate of Potash lias a very 
powerful action on tlie sulphides : in fact, if not modified by 
the addition of some inert substance, as an alkaline carbonate 
or sulphate, explosion may take place, and a portion of the 
contents of the crucible be thrown out. Where an excess 
of nitre is used, all the sulphur is converted into sulphuric 
acid, and every metal but gold and silver oxidised. When 
only the exact quantity of nitre is employed, that is to say, 
just as much as is sufficient to burn all the sulphur in the 
sulphide of those metals which are not very oxidisable, as 
those of copper, silver, and lead, the metal is obtained in a 
state of purity, and the whole of the sulphur converted into 
sulphuric acid ; but with the sulphides of the very oxidisable 
metals, the oxygen of the nitre is divided between the sul¬ 
phur and the metal. 

8 . Nitrate of Lead possesses the combined properties of 
nitre and litharge. It is not much used. 

9. Sulphate of Lead is not used as a reagent, but is often 
formed in the assay of lead ores. It decomposes sulphide 
of lead by burning the sulphur (Pb0,S0 3 + 2PbS = 3Pb 
-f 2S0 2 ). It acts on many other sulphides in a similar 
manner. 

IV. SULPHURISING REAGENTS. 

1. Sulphur. 

2. Cinnabar, or sulphide of mercury. 

3. Galena. 

4. Sulphide of antimony. 

5. Iron pyrites. 

6 . The alkaline persulphides. 

1. Sulphur fuses at 22G°, and at 284° is very liquid. It 
has very powerful affinities, and combines with the greater 
number of the metals. That kind generally known as flowers 
of sulphur ought to be employed; and before use, the pre¬ 
sence or absence of earthy matters should be ascertained, 
by exposing it to a dull red heat temperature in a crucible. 
The sulphur will go off, and the earthy impurities will be left 
behind. 


182 


SULPHURISING REAGENTS. 


Sulphur is principally used in the preparation of the 
alkaline sulphides and in the assay of some of the noble 
metals. 

2. Cinnabar is decomposed by many of the metals, and is 
a better sulphurising agent than sulphur itself, as it is less 
volatile. 

3. Galena. —Many metals, as iron, copper, &c., separate 
sulphur from lead, while some others, as silver, gold, &c., 
do not; so that if galena be heated with an alloy of various 
metals, some of which decompose it, and some do not, the 
former are transformed into sulphides, and the latter com¬ 
bine with the metallic lead which is produced. It is often 
employed for this purpose. It is a common ore, and readily 
procured. 

The samples employed must contain no sulphide of anti¬ 
mony, and all the matrix must be carefully separated by 
sifting and washing. 

4. Sulphide of Antimony yields its sulphur to many of 
the metals, but it is only used in the separation of gold from 
some alloys. In this operation the sulphur combines with 
the alloyed metals, and the antimony with the gold, for which 
it has much affinity. 

5. Iron Pyrites is a persulphide which loses half its sul¬ 
phur at a white heat. It is much employed in metallurgical 
operations, but not in assaying. 

6 . Alkaline Persulphides can support a tolerably elevated 
temperature without losing sulphur, but they have a great 
tendency to do so, and to this is due their sulphurising power. 
By their means almost every metal can be made to combine 
with sulphur. When an alkaline persulphide is heated 
with a metal, or an oxide of a metal mixed with charcoal, a 
fused compound, a mixture of the sulphide of the metal and 
an alkaline sulphide, is obtained. 

When they are in combination, they are held together by 
very feeble affinities, and their decomposition is generally 
effected by the mere action of water, which dissolves the 
alkaline sulphide and leaves the other perfectly pure. But 
with gold, molybdenum, tungsten, antimony, &c., the com¬ 
pound is stable and soluble in water ; and it is from this tact 


FLUXES. 


183 


tlicit the alkaline sulphides are sometimes employed in the 
assay of auriferous substances. 

In Older to effect a sulphurisation by means of the alka¬ 
line sulphides, it is much better to use equivalent mixtures of 
sulphur and alkaline carbonates than to prepare them before¬ 
hand. To obtain persulphide of potassium, 46 parts of car¬ 
bonate of potash, and 54 of flowers of sulphur, must be fused 
together; and for persulphide of sodium, 40 parts of dry 
carbonate of soda must be heated with 60 parts of sulphur. 

TV hen the mixture is fused in a plain crucible, sulphate 
of potash, or sulphate of soda, is formed, because part of the 
alkali is reduced to the metallic state by its affinity for the 
sulphur, giving up its oxygen to a portion of the sulphur, 
which becomes sulphuric acid ; but when charcoal lined 
crucibles are used, the carbon combines with the oxygen of 
the alkali, and no sulphate is produced. 


V. FLUXES. 

Fluxes are used in the following cases :— 

lstly. To cause the fusion of a body, either difficultly 
fusible, or infusible by itself. 

2ndly. To fuse foreign substances mixed with a metal, in 
order to allow the latter to separate by its difference of 
specific gravity. 

ordly. To destroy a compound into which an oxide enters, 
and which prevents the oxide being reduced by charcoal. 
Silicate of zinc, for instance, yields no metallic zinc with 
charcoal, unless it be mixed with a flux capable of combin¬ 
ing with the silica. 

4thly. To prevent the formation of alloys of some metals 
with others, as, for instance, in the case of a mixture of the 
oxides of manganese and iron ; when a suitable flux is em¬ 
ployed, the iron is obtained in a state of purity, whereas if 
no flux had been added an alloy would have been obtained. 
Gold and silver can be separated from many other metals 
by means of a flux. 

5thly. To scorify some of the metals contained in the 


184 


NON-METALLIC FLUXES. 


substance to be assayed, and obtain the others alloyed with 
a metal contained in the flux, as gold or silver with lead. 

6tidy. A flux may be employed to obtain a single button 
of metal, which otherwise would be obtained in globules. 

Fluxes are divided into non-metallic and metallic; the 
non-metallic fluxes are— 

1. Silica. 

2. Lime. 

3. Magnesia 

4. Alumina. 

5. Silicates of lime and alumina. 

6. Glass. 

7. Borax (biborate of soda). 

8. Fluor-spar (fluoride of calcium). 

9. Carbonate of potash. 

10. Carbonate of soda. 

11. Nitre (nitrate of potash). 

12. Common salt (chloride of sodium). 

13. Black flux and its equivalents. 

14. Argol (bitartrate of potash). 

15. Salt of sorrel (binoxalate of potash). 

16. Soap. 

The metallic fluxes are— 

17. Litharge (oxide of lead) and ceruse (carbonate of 

lead). 

18. Glass of lead (silicate of lead). 

19. Borate of lead; 

20. Sulphate of lead. 

21. Oxide of copper. 

22. Oxides of iron. 

1. Silica is employed frequently to cause the fusion of some 
gangues in assays made at an elevated temperature. Silica 
combines with all the bases, and forms with them bodies 
termed silicates, which are more or less fusible. 

Quartz is the best form of silica to use. For that purpose 
it must be strongly heated, and then quenched in cold 
water. It can then be easily pulverised. In case the quartz 


SILICA, LIME, BORAX. 


185 


takes a yellow or reddish colour on ignition, it must be 
digested with common muriatic acid. 

2, 3, 4, 5. Lime, Magnesia, Alumina, and their Silicates._ 

No simple silicate is readily fusible, so that lime, magnesia, 
or alumina are employed, according to circumstances, to 
reduce a simple silicate to such a condition that it will 
readily fuse in an assay furnace. Sometimes, it may be 
requisite to use all the above-mentioned earths. 

Pure lime, when exposed to atmospheric air, attracts 
carbonic acid and water so quickly that, in practice, pure 
carbonate of lime is used in the form of chalk, calcareous 
spar, or marble, if they are pure. Carbonate of lime fre¬ 
quently contains foreign substances, viz., iron, manganese, 
alumina, silica, and also carbonate of magnesia. A certain 
quantity of carbonate of magnesia is, in many cases, advan¬ 
tageous, and alumina and silica are not disadvantageous. 

Alumina is never used in the pure state. Washed china- 
clay which, on burning, becomes white, is used instead. 
Clay generally contains from 20 to about 40 per cent, alumina, 
and if it is used for the formation of silicates, a quantitative 
analysis of its components should first be performed. 

6. Glass is a very useful flux in certain assays, and being 
a saturated silicate, it will serve by itself either as a slag 
or merely as a covering. The kind employed must contain 
no easily reducible metallic oxides, and it must especially be 
free from arsenious acid and oxide of lead. 

The subjoined analyses of glass from Bode maim Kerbs 
Probierhunst will be found useful. (See p. 186.) 

7. Borax (Na0,2B0 3 + 10IIO and Na0,2B0 3 + 5110). 
—That kind with 10 atoms, or 47T per cent, water, efflo¬ 
resces when exposed to atmospheric air, and the other kind 
with 5 atoms or 30 per cent, water, does not effloresce, 
and crystallises in octahedrons. This difference is immaterial 
for assaying purposes, but it is of importance in purchasing 
borax. 

When borax is heated, it loses its water of crystallisation 
and undergoes an enormous increase of volume ; at a higher 
temperature, it fuses, and forms a transparent glass, which 
becomes dull on the surface by exposure to air. Only the 


ANALYSES OF DIFFERENT KINDS OF GLASS, 


186 


ANALYSES OF GLASS. 


pH 


o 

Cl 

< 


NONipOOH CO 
1C Tf 6 r-1 r—I !>• O O 


03 

o 

c3 

M 


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0) 

03 

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rH 


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o 

00 

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rH 

oo 



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o 


O CO 

rH 6 


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rH O 71 rH Cl 


b- p tj 

71 CO rH 


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Q 

a 


Cl 


CO 

6 


pi 

6 


o 

fco 


<71 

<71 


O 1C o 
6 6 bi 


O (71 
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oj 

o 


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71 07 CD O O O 


N O W Q b 


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CM <M 


lOOCOO^QOOOQO 

rH rH rH rH 71 rH 


07 

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71 






































FLUXES—FLUOR-SPAR, ALKALINE CARBONATES. 


187 


fused vitrified borax ought to be used in assays. It must be 
reduced to powder, and kept in well-closed vessels. 

As borax may be regarded as containing free boracic acid, 
it is an excellent and nearly universal flux; it has the property 
of forming, like boracic acid, fusible compounds with silica 
and nearly all the bases, and is preferable to that acid be¬ 
cause it is much less volatile. It may be used at a high or 
a low temperature. It is employed in the assay of gold 
and silver, because it fuses and combines with most metallic 
oxides, or in obtaining a reguius —that is to say, to separate 
the metals, their arsenides and sulphides, from any stony 
matter with which they may be mixed ; because this salt is 
neither oxidising nor desulphurising. It is also employed 
in the assay of iron and tin ores, as in the presence of 
charcoal it retains but traces of their oxides, and, indeed, 
much less than generally remains with the silicates. 

8. Fluor-spar (Fluoride of Calcium) is rarely employed 
in assays, but in certain cases is an excellent flux; as will be 
hereafter shown. 

9, 10. Carbonate of Potash and Carbonate of Soda.— 

It has been already shown that they possess oxidising and 
desulphurising power: they will now be considered as fluxes. 

They are decomposed in the dry way by silica and the 
silicates, with the separation of carbonic acid. The presence 
of charcoal much facilitates this decomposition. 

They form fusible compounds with many metallic oxides. 
In these combinations the oxide replaces a certain quantity 
of carbonic acid; but they are not stable—they are de¬ 
composed by carbon, which reduces the oxides, or by water, 
which dissolves the alkali. 

On account of their great fusibility, the alkaline carbonates 
can retain in suspension, without losing their fluidity, a large 
proportion of pulverised infusible substances, as an earth, 
charcoal, &c. 

The alkaline carbonates ought to be deprived of their 
water of crystallisation, for assaying purposes; in fact, it 
would be better to fuse them before use. They must in all 
cases be kept in well-stopped vessels. 

They may be used indifferently, but carbonate of soda is 


188 


FLUXES—NITRE, COMMON SALT. 


to be preferred, as it does not deliquesce, and is generally 
much cheaper. 

The alkaline carbonates of commerce always contain 
sulphates and chlorides. In some cases this causes no in¬ 
convenience, but there are many circumstances in which the 
presence of sulphuric acid would be injurious. 

Carbonate of potash can readily be procured free from 
sulphate and chloride by means of nitre and charcoal, as 
follows :—Pulverise, roughly, 6 parts of pure nitre, and 
mix them with 1 part of charcoal; then project the 
mixture, spoonful by spoonful, into a red-hot iron crucible. 
The projection of each spoonful is accompanied by a vivid 
deflagration, and carbonate of potash is found in a fused 
state at the bottom of the crucible. It must be pulve¬ 
rised, separated from excess of charcoal, and kept in a dry 
state for use. 

Carbonate of soda may be obtained in much the same 
way, substituting nitrate of soda for nitrate of potash. 
Either carbonate may also be obtained in a sufficient state 
of purity by repeatedly crystallising the commercial car¬ 
bonates. 

11. Nitrate or Potash. —Its properties have already been 
pointed out. The presence of silica or of silicates much 
assists its decomposition. 

12. Common Salt (Chloride of Sodium, NaCl) is recom¬ 
mended either mixed with flux, or placed above it, for the 
purpose of preserving the substance beneath from the action 
of the atmosphere, or to moderate the action of such bodies 
as cause much ebullition. It is very useful in lead assays, 
and is much used in the assay of silver by the wet way. 
It must be previously pounded, and heated to dull redness 
in a crucible, to prevent its decrepitation. 

Common salt, though containing sulphates, chlorides of 
calcium, and magnesium, is in most cases sufficiently pure 
for assaying purposes. If intended for copper assays, it must 
be previously purified from sulphates. 

Plattner * has examined the influence of common salt upon 
different oxides and sulphates. It does not act upon un- 

* B. u. h. Ztg. 1854, p. 126. 


BLACK, WHITE, AND RAW FLUX. 


189 


combined oxides of lead and zinc. Sulphate of lead, when 
melted with it at a dull red heat, becomes liquid, and evolves 
vapour of chloride of lead. By raising the temperature, 
and by giving more draught of air, the evolution of such 
vapour is increased. Common salt acts upon sulphate of zinc 
in the same way. Oxide of antimony and antimonious acid 
heated with it at a dull red heat evolve vapour of chloride 
of antimony though not in a great quantity. Sulphate of 
copper melted with salt at a red heat becomes converted 
into chloride of copper and sulphate of soda. Chloride of 
copper becomes vaporised if air is admitted, and it becomes 
converted into subchloride of copper by raising the tempera¬ 
ture a little, chlorine being then evolved. 

13. Black Flux, White Flux, and Raw Flux. — White flux 
is produced by deflagrating together equal parts of saltpetre 
and argol (crude bitartrate of potash); black flux , by de¬ 
flagrating one part of saltpetre with two or three or more 
parts of argol. Generally one part of saltpetre and two and 
a half parts of argol are taken. The finely pulverised and 
intimate mixture for either flux, before it is deflagrated, is 
called raw flux. 

After the saltpetre and argol have been finely pulverised 
and sifted separately, they are intimately rubbed together, 
and then deflagrated by throwing the mixture little by little 
into a low-red-hot crucible, which after each addition is 
lightly covered over. The deflagration may also be con¬ 
ducted, though less advantageously, by filling the crucible 
about two-thirds full of the raw flux and then touching it 
with a red-hot coal or iron. It can only be performed in 
the open air or under a flue with a strong draft, as the tar¬ 
taric acid evolves various empyreumatic volatile matters in 
considerable quantity during its decomposition. 

With white flux the saltpetre suffices to burn all the charcoal 
produced by the carbonisation of the tartaric acid, and the 
result is therefore almost pure carbonate of potash, if pure 
saltpetre and pure argol have been used. If the latter were 
impure, the resulting neutral carbonate of potash may 
contain much, perhaps 10 per cent., of carbonate of lime. 
White flux works like ordinary carbonate of potash, which 



190 BLACK, WHITE, AND RAW FLUX. 

is therefore almost always preferred to the far more expen¬ 
sive flux. 

With the black flux the quantity of saltpetre is not suffi¬ 
cient to burn all the coal from the argol, and there remain 
therefore in the black flux, according as two, two and a 
half, or three parts of argol were taken, about 5, 8, or 
12 per cent, of free carbon, which is mixed in the most 
intimate manner with the resulting neutral carbonate of 
potash—more intimately indeed than would be possible by 
any mechanical means. This charcoal does not hinder the 
fusing of the assay when the flux is used, and effects or pro¬ 
motes the reduction of the metallic oxides. 

Fusion and reduction, sometimes also desulphurisation, 
are the purposes for which black flux is used, and, accord¬ 
ing to the special character of the assay, a greater or a less 
proportion of charcoal to the carbonate of potash may be de¬ 
sirable, and this is to determine whether two, two and a half, 
three, or more parts of argol are to be used to one of saltpetre. 
As a general rule it may be stated, the more difficultly 
fusible is the assay, the more potash ; and the more metal¬ 
lic oxide is to be reduced, the more charcoal; and the more 
also of the latter, the more oxygen the oxide contains. 

In many cases, instead of black flux, a mixture of car¬ 
bonate of potash and powdered charcoal, in a suitable ratio 
to cacli other, suffices, especially if the mixture, before use, 
is passed through a sieve, or otherwise very intimately 
mingled. Instead of the powdered charcoal, also, a corre¬ 
sponding (about two to four times as large) quantity of flour, 
or sugar, or starch may be mixed with the carbonate of 
potash. Lamp black is, however, the best form of carbon. 
The three following fluxes are very useful :— 

Carbonate of soda. 94 88 816 

Charcoal.G 12 184 

The second is very nearly equivalent to sodium and car¬ 
bonic acid, and the third to sodium and carbonic oxide; but 
it must be observed, that whatever precautions be taken, 
these mixtures never become so liquid as black flux, because 
the charcoal tends very much to separate and rise to the 
surface. 


FLUXES—CREAM OF TARTAR, SALT OF SORREL. 191 

A mixture of 100 parts of pure carbonate of potash and 
10 to 15 parts of wheat or rye flour is to be preferred to 
black flux in case the argol contains gypsum, or the salt¬ 
petre, sulphates, which in many cases might work injuriously 
upon the assay. If this is the case, then, in the presence of 
a reducing flux, sulphide of sodium is apt to form, which, 
for example in the copper assay, occasions the slagging of 
copper. 

Cream of tartar, carbonised by a semi-combustion until it 
is reduced to half its weight, is a very good substitute for 
black flux ; it contains about 10 per cent, of charcoal. 

As a perfectly general rule for the use of black flux, 
and of mixture similar to it, it is to be observed that the 
crucible should never be more than two-thirds filled, as the 
assay always intumesces, i.e. evolves gaseous matters, when 
free carbon is present. 

14. Argol, Cream or Tartar, or Bitartrate of Potash.— 

When bitartrate of potash is heated in a covered crucible, 
a rapid decomposition takes place, accompanied by a disen¬ 
gagement of inflammable gases : the substance agglome- 
rates, but without fusing or boiling up. The residue is 
black and friable, and contains 15 per cent, of carbon when 
produced from rough tartar or argol, and 7 per cent, from 
cream of tartar. 

These reagents produce the same effects as black flux, 
and possess more reducing power, because they contain 
more combustible matter: but this is an inconvenience, for 
the excess prevents their entering into full fusion when the 
substance to be assayed requires but a small proportion of 
a reducing agent. They can be used with success in assays 
requiring much carbonaceous matter. 

15. Salt of Sorrel, or Binoxalate of Potash, when heated, 
is decomposed. It decrepitates feebly, and during its de¬ 
composition is covered with a blue flame; it at first softens, 
and when fully fused is wholly converted into carbonate. 
When the oxalate is very pure, the resulting carbonate is 
perfectly white, and free from charcoal : but very often it 
is spotted with blackish marks. It has no very great re¬ 
ducing power. 


192 


FLUXES—SOAP. 


1G. White, or Mottled Soap, is a compound of soda with a 
fat acid. When heated in closed vessels it fuses, boiling up 
considerably, and during its decomposition gives off smoke 
and combustible gases, and leaves a residue composed of 
carbonate of soda with" about 5 per cent, of charcoal. Of 
all reducing agents, soap absorbs the greatest quantity of 
oxygen; and, as the residue of its decomposition by heat 
affords but little charcoal, it has the property of form¬ 
ing very fluid slags. Nevertheless, it is rarely employed, 
because certain inconveniences outweigh its advantages. 
These inconveniences are, its bubbling up, and its extreme 
lightness. It also requires to be rasped, in order to mix it 
perfectly with the substances it is to decompose, and it then 
occupies a very large volume, and requires correspondingly 
large crucibles. By mixing rasped soap with binoxalate of 
potash or carbonate of soda, excellent reducing fluxes may 
be made :— 

Salt of sorrel . . Sol Q Q _ 

Soap . . . 15 J * * * * * 

Carbonate of soda .851 0 

Soap . . . 15 J * * ' * * ^ 


Reducing Power of the various Fluxes .—By fusing equal 
weights of each of the above-mentioned reducing fluxes with 
an excess of litharge, the following quantities of lead were 
yielded :— 


Common black flux, made with two parts of tartar 
Ditto, with 2£ of tartar 
Ditto, with 3 of tartar 
Carbonate of soda 


Charcoal . 

Carbonate of soda 
Charcoal . 

Carbonate of soda 
Sugar 

Carbonate of soda 
Sugar 

Carbonate of soda 
Starch 

Carbonate of soda 
Starch 

Crude tartar, argol 
Cream of tartar . 
Ditto, ditto, carbonised 
Ditto, ditto, calcined 
Binoxalate of potash 
White soda soap 


941 

Of 

88 
12 
90 
10 
80 
20 
90 
10 
80 
20 


1-40 

1-90 

3-80 

1*80 


300 


1-40 


2-80 


1- 15 

2- 30 

5-00 

4-50 

310 

2-20 

•90 

10-00 





METALLIC FLUXES. 


193 


All fluxes containing alkaline and carbonaceous sub¬ 
stances are reducing and desulphurising, besides acting as 
fluxes, properly so called. They also produce another 
effect which it is useful to know, viz. they have the pro¬ 
perty of introducing a certain quantity of potassium or 
sodium into the reduced metal. This was first pointed out 
by M. Vauquelin.* He found that when oxide of antimony, 
bismuth, or lead, was fused with an excess of tartar, the 
metals obtained possessed some peculiar characters, which 
they owed to the presence of potassium. 


METALLIC FLUXES. 

17. Litharge and Ceruse. —These bodies always act as 
fluxes, but at the same time often produce an alloy with 
the metal contained in the ore to be assayed. Ceruse 
produces the same fluxing effect as litharge. The former 
is the better flux, and is very useful in a great number of 
assays. 

18. Glass of Lead ( Silicate of Lead). —The silicates of 
lead are preferable to litharge in the treatment of substances 
containing no silica, or which contain earths or oxides not 
capable of forming a compound with oxide of lead, except¬ 
ing by the aid of silica. It may be made by fusing 1 part 
of sand with 4 parts of litharge : if required more fusible, 
a larger proportion of litharge must be added. 

19. Borate of Lead. —The borates of lead are better 
fluxes than the silicates when the substance to be assayed 
contains free earths ; but in order to prevent them swelling 
up much when fused, they must contain an excess of oxide 
of lead. The borate of lead containing 90*56 of oxide of 
lead and 9*44 of boracic acid, is very good. Instead of 
borate of lead, a mixture of fused borax and litharge may 
be employed ; it is equally serviceable. 

20. Sulphate of Lead is decomposed by all siliceous 
matters, and by lime, so that when these substances are 
present litharge is produced, which fluxes them. 

* Annales des Mines. 

0 



194 


METALLIC FLUXES. 


21. Oxide or Copper is rarely used as a flux for oxidised 
matters, but is sometimes employed in the assays of gold 
and zinc, to form an alloy with those metals. In this case 
a reducing flux must be mixed with the oxide. Metallic 
copper may be used, but is not so useful, as it cannot be so 
intimately mixed with the assay. 

22. The Oxides of Iron are good fluxes for silica and 
the silicates. They are, however, rarely employed for that 
purpose; they are more often used to introduce metallic 
iron into an alloy to collect an infusible, or nearly infusible, 
metal, by alloying it with iron ; such as manganese, tungsten, 
or molybdenum. 


CHAPTER VII. 


THE BLOWPIPE AND ITS USE. 

The blowpipe was formerly only used by jewellers and 
workers of metal for producing sufficient heat for soldering 
certain small portions of their work ; and it was not till about 
the year 1733, that Anton Swab applied it to the analysis 
of mineral substances. Cronstedt used the blowpipe to 
ascertain the difference between various mineral substances 
as to fusibility, &c. In 1765, Von Engestrom published 
Cronstedt’s System of Mineralogy, and added to it a Treatise 
on the Blowpipe, in which he pointed out the processes of 
Cronstedt. 

This work attracted the attention of philosophers to this 
valuable instrument, and its use became more general. 
Bergman, after Cronstedt, extended the use of the blowpipe 
beyond the bounds of mineralogy to the inorganic kingdom, 
and in his hands this instrument became an invaluable 
agent for the detection of minute portions of many metallic 
substances. Bergman treated the greater number of the 
minerals known in his time with the reagents employed by 
Cronstedt, described their action, and improved many of 
the instruments necessary for their performance. In these 
experiments, Bergman, whose health did not permit him to 
carry out such a laborious work, was assisted in his minera- 
logical studies by Gahn, who became particularly expert in 
the use of the blowpipe. The following is a very good 
example of the utility of this instrument in practised hands : 

4 Ekeberg asked Gahn his opinion of the then newly dis¬ 
covered mineral, the oxide of tantalum, and Gahn imme¬ 
diately discovered that it contained tin, although it did not 
amount to more than 1 per cent.’ 

o 2 


190 


THE BLOWPIPE AND ITS USE. 


Berzelius, after Gahn, was particularly famed for his skill 
with the blowpipe, and for his improvements in the form of 
apparatus; and it is from his excellent work on this subject 
that the principal portion of the descriptive part of Blow¬ 
pipes, Lamps, Tongs, &c., is derived. 

The common blowpipe of gas-fitters, jewellers, &c., is a 
tube of brass, tapering towards one end, and curved at that 
extremity, which has an opening as fine as that made by 
the finest needle ; it is this opening which is held against 
the flame of the lamp, and air is blown to it to increase the 
amount of heat. In all ordinary operations, the blast is 
required to be kept up not more than a minute, so that the 
quantity of moisture exhaled from the lungs produces no 
inconvenience by stopping up the tube. But in certain 
chemical operations, this is exceedingly troublesome, as a 
continuous blast is required, and a large quantity of water 
collects in consequence, generally sufficient to mar the 
success of an experiment. In order to obviate this, Cron- 
stedt placed in the centre of his blowpipe a bulb, in which 
the greater part of the water collected. This form was, 
however, inconvenient, because if the jet of the blowpipe 
were at all inclined, even for an instant, the water ran from 
the bulb, and filled it. In a series of articles communicated 
to the 4 Chemical News,’ Mr. David Forbes, F.B.S, has given 
directions which are invaluable to all who practise with 
this instrument. From these we quote the following :— 

4 Blowpipe. —The form adopted long ago by Gahn is con¬ 
sidered, however, as the most convenient. Fig. 66 shows 
an improvement made by the author upon this form. 

4 In this figure it will be seen that the arm of the jet is 
double, turning upon a central hollow axis, which allows 
the blast to be directed at will through either half of the 
arm, merely by rotating the arm itself half round ; by having 
consequently the two holes with respectively a large and 
small orifice, a corresponding blast may be obtained at 
pleasure, without suspending the operation. 

4 As a more steady and long-continued blast is required 
in quantitative operations than could be kept up by using 
a blowpipe provided with an ordinary mouthpiece held 


MR. FORBES’S BLOWPIPE. 


197 


Fig. 66. 


between the lips, without seriously distressing the muscles 
of the cheeks, it is quite essential that the trumpet mouth¬ 
piece, shown in Fig. 66, be 
adopted ; for the same reasons 
also the mode of holding the 

O 

blowpipe represented in Fig. 67, 
is recommended, as securing the 
greatest steadiness from motion, 
and as greatly assisting the 
muscles of the cheeks by tlie ex¬ 
ternal support afforded them 
by the position of the thumb 
pressing against the trumpet 
mouthpiece.’ 

The nipples are turned, and 
bored of three different sizes, 
and are made both of platinum 
and of brass. The first, of 
platinum, contains the smallest 
apertures, and is employed for 
qualitative analysis ; the second, 
of brass, is used for such quali¬ 
tative experiments as require a 
strong oxidising flame, and for 
heating silver, gold, arid copper, 
in quantitative assay ; also for 
roasting copper, lead, and tin- 
ores, the metallic contents of 

which are to be accurately determined ; and the third, which 
is also manufactured of brass, has the largest bore, and is 
used for the quantitative estimation of Fig. 67. 

lead and tin. 

Platinum nipples are, however, al¬ 
ways preferable to those of brass, be¬ 
cause by exposure to a moderate red 
heat on charcoal before the blowpipe, 
they are more easily cleaned from 
the sooty particles which obstruct the aperture. Tina 
method of cleansing cannot be applied to brass nipples, 









198 


BLOWPIPE LAMP. 


owing to their rapid oxidation ; to clean these the operator 
must adapt to the opening a sharp-pointed fragment of horn, 
or a small needle, ground along one half of its length ; by 
this means the aperture through which the air passes may 
be readily cleaned. 

Many persons imagine that the use of the blowpipe is 
very injurious. Hence, various contrivances have been 
made to use this instrument by other means ; some have 
employed double bellows, others bladders, and others, again, 
the pressure of water ; but none of these methods have 
afforded satisfactory results, except in the hands of the 
contrivers, and even in those cases the results have sometimes 
been very problematical. 

Any kind of flame may be used for the blow-pipe, pro¬ 
vided it be not too small; a candle, a lamp, or gas, may be 
employed : Engestrom and Bergman used common candles 
in preference. Berzelius employs a, lamp, which is certainly 
much preferable to a candle. I have occasionally employed 
the flame of coal gas, which answers very well, but is not 
so good as that of a lamp. Berzelius says on this subject, 

‘ Lamps have doubtless many advantages over candles, but 
are not so convenient in travelling, on account of the 
escape of oil. The oil employed ought to be the best olive 
or salad oil. 

4 The lamp which I use has the advantage of being port¬ 
able, and closes in such a manner that no oil can escape. 
It is made of japanned tin-plate, and is about 4 inches 
long, and 1 inch wide, furnished at one end with a wick- 
holder, capable of being completely closed by a screw, and 
at the other with a ring of tin-plate, which passes over the 
upright end of a support. It may be mentioned, that the 
screw-cap is furnished with a leather washer, by the aid of 
which it can be rendered much tighter, and the escape of 
oil entirely prevented.’ 

Mr. Forbes says that olive-oil, burnt in the usual Berze¬ 
lius blowpipe lamp, is probably superior to any other. Gas 
is not to be recommended, as it is difficult to obtain a good 
reducing flame when using it. For cupellation and such 
other operations, however, which only require an oxidating 
flame, it is excellent. 


USING THE BLOWPIPE. 


199 


A spirit-lamp may sometimes be employed in blowpipe 
assays, particularly when glass tubes are employed, as in the 
detection of volatile substances. In these cases it is much 
more convenient; as an oil-lamp, in the first place, blackens 
the tube; and secondly, does not yield sufficient heat, 
except when the blowpipe blast is employed. 

It is very difficult to give in writing a method whereby a 
student may acquire the practice of using the blowpipe: 
that given by the late Professor Faraday * is perhaps the 
clearest and most concise. He says, 4 The practice necessary, 
in the first place, is that of making the mouth replace the 
lungs for a short time, by using no other air for the blow¬ 
pipe than that contained in it.’ This practice is simple in 
itself, and easy to acquire, but, as before stated, difficult to 
describe. Let the student first observe, that it is easy after 
having closed the lips to fill the mouth with air, and to 
retain it so, at the same time that respiration may be carried 
on; and if, while the mouth is in this state, a blowpipe be 
introduced between the lips, it w T ill be found that the small 
quantity of air which its jet allows to pass through it, will be 
amply supplied for ten or fifteen seconds by the quantity 
contained in the mouth ; and this being repeated a few times, 
a ready facility for using the blowpipe, independent of the 
lungs, will be acquired. 

This step being taken, the next is to combine this process 
w r ith the ordinary one of propelling air directly from the 
lungs througli the mouth, in such a way that when the action 
of the lungs is suspended during inspiration, the blast may 
be continued by the action of the mouth itself, from the air 
contained within it. The time of fourteen or fifteen seconds, 
during which the mouth can supply air independently of the 
lungs, is far more than that required for one or even many 
more inspirations ; and all that is required to acquire the 
necessary habit is the power of opening and closing the com¬ 
munication between the mouth and the lungs, and between 
the air and the lungs, at pleasure. 

The capability of closing the passages to the nostrils is 
very readily proved : .every one possesses and uses it wffien 


* ‘ Chemical Manipulation.’ 


•200 USING THE BLOWPIPE. 

he blows from the mouth, and that of closing or opening the 
mouth to the lungs may be acquired with equal readiness. 
Applying the blowpipe to the lips as before, use the air in 
the mouth to produce a current, and when it is about half 
expended, open the lungs to the mouth, so as to replace the 
air which has passed through the blowpipe ; again cut off the 
supply, as at first, but continue to send a current through 
the instrument, and when the second mouthful of air is gone, 
renew it as before from the lungs. 

To some this may be difficult; but if the preceding 
instructions be followed and persevered in for a short time, 
the learner will soon find that he can keep up a continuous 
blast from ten minutes to a quarter of an hour, without any 
other inconvenience than the mere lassitude of the lips, 
caused by compressing the mouthpiece of the instrument, 
and this may be avoided by using the trumpet mouthpiece 
as recommended by Mr. Forbes. 

After having conquered the difficulty of keeping up a con¬ 
tinuous blast, the student must learn how to attain the 
maximum of heat with the least exertion to himself. The 
chief points to be observed are, neither to blow too fiercely 
nor too gently ; in the first case, the force of the blast would 
carry away heat by the quantity of cold air thrown into the 
flame, and in the second, a sufficient amount of heat would 
riot be obtained ; because a less amount of air would pass 
into the flame than that required for perfect combustion. 

The highest degree of temperature is required in testing 
the fusibility of many bodies, as also in the reduction of 
certain oxides, as those of iron, tin, &c. We have yet 
another class of phenomena to describe, which do not essen¬ 
tially depend on a high temperature ; these are the processes 
of reduction and oxidation. In order to explain and point 
out the best methods of effecting these two objects, it will be 
necessary to enter somewhat into the nature of flame : this 
will be done as briefly as is consistent with perspicuity. 
The species of flame examined will be that of a candle, a’s it 
is with a .similar one to that with which the blowpipe 
operator will have to experiment. 

On careful examination, it will be found that the flame of 



REDUCTION AND OXIDATION. 


a candle or lamp maybe divided into four distinct ; portions 
firstly, a deep blue ring at the base ; this consists of the 
vapour of the combustible, which can hardly burn because it 
has not acquired a sufficient temperature; secondly, a dark 
cone in the centre ; this is also the vapour, but heated in¬ 
tensely, not, however, in a state of combustion, on account 
of the absence of air; thirdly, of a very brilliant envelope, 
which surrounds the dark parts just mentioned ; this is the 
partially consumed vapour at a very high temperature ; the 
luminous property it possesses is due to the precipitation 
and subsequent ignition of particles of solid carbon; and 
fourthly, of an almost invisible envelope which surrounds 
the luminous portion ; this is the substance of the com¬ 
bustible in full ignition, it here mingles with the atmo¬ 
spheric oxygen, and is consumed. The highest degree of 
temperature in the whole flame is to be found at the point 
of contact between the luminous and this part. It must be 
particularly borne in mind that the inner portions of the 
flame have an excess of carbonaceous matters, and the outer 
an excess of oxygenated matters. 

Having premised thus much, we will examine the nature 
of the flame of a candle when acted on by the blowpipe 
blast, and ascertain how far it is altered, and what are 
the properties of its separate parts in relation to their 
oxidising and reducing powers. Supposing the lighted 
lamp or candle be ready and neatly snuffed, place the nozzle 
of the blowpipe just in the edge of the flame, and about 
the sixteenth of an inch above the level of the wick : when 
things are in this state, blow gently and evenly through 
the blowpipe, and a conical jet or dart of flame will be 
produced, which, when formed in a steady atmosphere, free 
from accidental draughts and currents, will be found to 
consist of two essential parts—the inner cone, blue, small, 
and well defined ; the outer, brownish and vague. The 
greatest intensity of heat is found a little beyond the apex 
of the blue flame ; it is there, also, reduction takes place. 
The outer flame is formed by the complete combustion of 
the combustible matter of the inner; and at that place, and 
just beyond it, oxidation takes place. 


202 


AUXILIARY BLOWPIPE APPARATUS. 


Oxidation , as before stated, takes place at the extremity 
of the outer flame, lienee it is termed the oxidising flame ; 
in it all the combustible portions are super-saturated with 
oxygen. In general the further the substance to be oxidised 
can be placed from the extremity of the flame, the better the 
operation proceeds, provided always that the necessary tem¬ 
perature be maintained. Dull redness is the best suited 
for oxidation. 

Reduction .—In this operation the jet of the blowpipe must 
be introduced into the body of the flame, so as only to produce 
a small dart; and a jet having a smaller hole than that used 
for oxidation ought to be employed. By operating thus, a 
more brilliant flame than the last is produced ; it is the result 
of a less perfect combustion, and therefore contains a large 
amount of carbonaceous matter, fitting it more especially for 
the purpose of separating oxygen from all metallic bodies. 

Berzelius says, 6 the most important point in blowpipe 
assays is the power of producing oxidation and reduction at 
will.’ Oxidation is so easy, that to do it requires only to 
read a description of it; but reduction requires some 
practice, and a certain knowledge of producing various kinds 
of blasts. One of the best methods of exercise in this 
operation is to take a small grain of tin, and place it on 
charcoal; then direct the blowpipe dart upon it—it will 
soon fuse; and if the operator has not produced a good 
reducing flame, it will become covered with a crust of 
oxide ; so that it becomes a witness against him each time 
this happens. The nature of the flame must be altered 
until, by observation, the proper kind is produced at will. 
The longer the button of tin is kept bright, the better and 
more expert the operator. 

AUXILIARY BLOWPIPE APPARATUS, ETC. 

Supports .—The support is the substance destined to hold 
the material to be assayed whilst under the influence of 
heat. From this it will be seen that a solid body must 
necessarily be employed: it ought also to be exceedingly 
refractory, so as not to give way under the excessive heat; 
and lastly (with the exception of charcoal), ought to have 


CHARCOAL APPARATUS. 


203 


no chemical action on the substances placed in contact with 
it. Supports may be divided into combustible and in¬ 
combustible ; the former is charcoal, and for the latter, 
metal, glass, and earthenware, and in some cases certain 
minerals have been employed. 

Charcoal .—Mr. Forbes gives the following excellent 
description of the preparation of charcoal for blowpipe 
purposes. ‘ It is extremely difficult to obtain, in England, 
charcoal lit for blowpipe operations, without special pre¬ 
paration. The charcoal sold is generally of hard wood, 
badly burnt, full of cracks, and decrepitating upon appli¬ 
cation of heat. Good charcoal should be soft, yet compact, 
and without cracks, and is best made from fir or pine. 
Where good charcoal cannot be obtained it can be made 
artificially by moulding charcoal powder agglutinated by 
some starch paste, and, after desiccation, burning the pieces 
in a crucible filled with sand. 

4 For the preparation of the charcoal used as a support 
for the assays, the instruments represented in fig. 68 are re¬ 
quired, all of which are fitted in the universal handle a, 
which is shown in this figure 
as holding the largest charcoal 
borer, a section and plan of 
which are shown in b. This 
large borer is employed for 
forming the deep holes in the 
charcoal used in the blowpipe 
furnace, and which serve to 
contain the clay crucibles or 
capsules in which the assays are 
fused. The blast holes in the 
charcoal inside the blowpipe 
furnace are bored out by the 
gouge-shaped borer cl , which 
also serves for making small 
holes or grooves in charcoal for 
general purposes. The smaller 
borer c, is most useful, particularly in boring out the holes 
for receiving the soda paper cornets containing the assay for 
reduction. The saw-knife e also fits into the same handle, 


Fig. 68. 










204 


AUXILIARY BLOWPIPE APPARATUS. 


and is used for trimming and sawing across the charcoal 
pieces, having coarse saw teeth in front, whilst the back 
presents a sharp knife edge. The figures are all drawn to 
one-half of the real size.’ 

Platinum .—This metal is much employed as a support in 
cases where charcoal would be injurious by its reducing 
power. It is used in three forms, viz. wire, foil, and as a 
spoon, or small capsule. 

Wire .—A moderately strong wire of platinum, about 2 
inches long, and curved at one end, is used with great 
advantage in many quantitative examinations. The curve 
serves as a support in all experiments on tests of oxidation 
and reduction, where alteration of colour only is to be 
observed. This support can be relied on, for it is totally 
free from the false varieties of colour which are too often 
perceptible when the assay rests on charcoal. In the 
treatment of metals, or in reduction tests, where an easily 
melted body is to be operated upon, charcoal must, however, 
be used. It is necessary to have at hand several platinum 
wires, so as to proceed to another experiment without being 
obliged to forcibly remove the adhering borax glass, or to 
wait for its solution in hydrochloric acid, which is the better 
mode. If the platinum loop melts with the reagent, it must 
be cut away, and a new one formed. A wire can be used 
for a very long time, and when it becomes too short to be 
held between the fingers the straight end may be fastened 
into a cork, or a piece of glass tubing. 

The platinum spoon (see fig. 69) and foil are used in 
much the same way; but as charcoal and the platinum wire 
Fig. 69 . answer every purpose, it 

will be unnecessary to de- 

•/ 

scribe their use further : 
small iron spoons of the 
above form are also made, 
and are very useful incases 
where the presence of iron 
is not objectionable. 

Other instruments, as forges, hammer, anvil, agate mor¬ 
tar, scissors, &c., are sufficiently familiar to everybody not 







FLUXES AND REAGENTS 


205 


to require description. Special apparatus required for any 
operation will be described in the course of the processes. 

Fluxes and Reagents. —dhese most important bodies may 
be classified under two heads : reagents in the humid way 
and reagents in the dry way. For the sake of clearness and 
simplicity, these two classes are subdivided again. 

I. REAGENTS IN THE HUMID WAY. 

a. Reagents used as Simple Solvents. 

1. Distilled Water. —Principally used as a simple solvent 
for a great variety of substances. It also effects the trans¬ 
formation of several neutral metallic salts (antimony, bis¬ 
muth) into soluble acid and insoluble basic compounds. 

2. Alcohol. —It is frequently employed for separating the 
substances soluble from those insoluble in it (chlorides of 
barium and strontium) ; for precipitating bases from their 
aqueous solutions ; for detecting various substances, especially 
boracic acid, strontia, soda, &c. 

3. Ether is principally employed for dissolving bromine. 

b. Reagents principally employed as Chemical Solvents. 

1. Hydrochloric Acid is extensively used as a solvent, 
and for the detection of silver, suboxide of mercury, lead, 
and ammonia. 

2. Nitric Acid is employed in the solution of various 
metals, alloys, and ores, and for the discrimination of certain 
precipitates. Also as an oxidising agent. 

3. Nitro-liydrochloric Acid. —Principally used as a solvent 
for gold and platinum. 

4. Acetic Acid. —This acid possesses a greater solvent 
power for certain substances than others, and is accordingly 
used to separate the former from the latter; as, for distin¬ 
guishing oxalate of lime from phosphate of lime; the latter 
being easily dissolved, while the former remains unaltered. 

5. Chloride of Ammonium. —Used for retaining certain 
salts and oxides in solution, when others are precipitated by 
ammonia or some such reagent as magnesia, which is 



206 


FLUXES AND REAGENTS. 


held in solution by ammonia and chloride of ammonium, 
when baryta, strontia, and lime are precipitated by carbonate 
of ammonia. 

c. Reagents used to separate, or otherwise characterise, 

Groups of Substances. 

1. Reagent papers. 

a. Blue Litmus Paper, for detecting free acid in solution, 
its colour being changed to red. 

b. Redde?ied Litmus Paper, for the detection of free alkali, 
its colour being restored to blue. 

c. Brazil-wood Paper, for detecting hydrofluoric acid, 
being tinged straw-yellow when immersed in a very dilute 
solution of this acid. 

d. Turmeric Paper, for detecting free alkalies ; the change 
produced is very characteristic, its bright yellow colour be¬ 
coming dark brown. 

2. Sulphuric Acid has a greater affinity for most bases 
than any other acid, and is, consequently, employed for 
liberating them. It is a special test for the detection of 
baryta, strontia, lead, lime, &c. 

3. Sidphuretted Hydrogen is an invaluable reagent for 
separating metals into the principal groups. 

4. Sulphide of Ammonium divides those metals which 
are precipitated by sulphuretted hydrogen into two groups; 
it is also the precipitant of the third group. 

5. Solution of Potash. —As a precipitant for many oxides 
it is invaluable. Is used in the separation of iron from 
alumina, as also nickel from cobalt. 

6. Ammonia is much employed in the precipitation of 
metallic oxides, neutralisation of acids, &c. 

7. Carbonate of Ammonia is employed as a test for many 
of the earths ; it is also used in the removal of an excess of 
acid from a solution. 

8. Chloride of Barium. —A special reagent for sulphuric 
acid. It is also a valuable reagent for subdividing the preci- 
pitable acids. 

9. Nitrate of Baryta acts the same as chloride of barium. 


FLUXES AND REAGENTS. 


207 


and is substituted for that reagent where the presence of a 
metallic chloride would be deleterious. 

10. Chloride of Calcium precipitates, as a group, from 
neutral solutions, phosphoric, hydrofluoric, oxalic, tartaric, 
and citric acids ; also, if the solution is not very dilute, sul¬ 
phuric acid. 

11. Nitrate of Silver. —This is a very important reagent 
for the classification of acids into groups, and is employed 
for the detection of certain individual acids, especially hydro¬ 
chloric, phosphoric, and arsenic acids. 

12. Sesquichloride of iron , as the reagent for a group of 
organic acids. It is also employed for the detection of 
hydroferrocyanic acid in the formation of Prussian blue. 


d. Reagents used for the Detection of Bases. 

1. Sulphate of Potash precipitates from solutions of salts 
of baryta and strontia the insoluble sulphates of these bases. 
It also produces a precipitate in concentrated solutions of 
lime, but only after some time. 

2. Chromate of Potash precipitates from solutions of 
the salts of many metallic oxides, chromates ; most of them 
are very difficultly soluble, and possess characteristic colours, 
by which the particular metal may often be with certainty 
detected. It is used, principally, however, as a test for 
lead, with which it gives a yellow precipitate. 

3. Cyanide of Potassium. —This is a most useful flux. 
MM. Haidlen and Fresenius say: ‘We have examined its 
action on many oxides, sulphurets, salts, &c., in reference to 
its use as a reagent combined with the blowpipe. We 
prefer, in general, a mixture of equal parts of anhydrous 
soda and cyanide of potassium. This mixture was employed 
on account of the great facility with which the pure cyanide 
fuses. It acts, in general, so very similarly to pure soda, 
that it would be superfluous to describe singly the changes 
which each individual body appeared to undergo when 
exposed to its action. We cannot, however, pass over the 
following especial advantages which it possesses as compared 
with soda. Firstly, reductions are obtained with such 



208 


FLUXES AND REAGENTS. 


great facility that the least practised operator may execute 
reductions which would otherwise be very difficult; for 
instance, the reduction of tin from either its oxide or 
sulphuret; and, secondly, that the fused mixture of cyanide 
of potassium with soda is so easily absorbed by the charcoal, 
that the grains of reduced metal can always be most 
distinctly perceived, and may be most easily separated 
therefrom for further examination.’ 

Pure cyanide of potassium may be made by heating dry 
ferrocyanide of potassium to whiteness in close iron vessels, 
and dissolving the cyanide in alcohol of 60 per cent.; but 
the salt in its pure state is not used as a blowpipe reagent; 
it is the mixture of cyanide of potassium with cyanate of 
potash, formed in the readiest manner by Liebig’s process, 
which may be thus conducted. Eight parts of ferrocyanide 
of potassium are rendered anhydrous by a gentle heat, and 
intimately mixed with three parts of dry carbonate of pot¬ 
ash ; this mixture is thrown into a red-hot earthen crucible, 
and kept in fusion, with occasional stirring, until gas ceases 
to be evolved and the resulting mass becomes colourless. 
The crucible is left at rest for a moment, and the clear salt 
decanted from the heavy black sediment at the bottom. 
The ferrocyanide and the carbonate employed ought to be 
perfectly free from sulphuric acid. 

4. Ferrocyanide of Potassium. —Principally used for the 
detection of oxide of copper, and for indicating the presence 
of sesquioxide of iron. 

5. Ferrocyaiiide of Potassium is used as a test for prot¬ 
oxide of iron and its salts. 

6. Sulphocyanide of Potassium , used like ferrocyanide of 
potassium, for the detection of sesquioxide of iron. 

7. Phosphate of Soda. —It precipitates all the alkaline 
earths, but is chiefly employed, after the separation of 
baryta, strontia and lime, for the detection of magnesia. 

8. Oxalate of Ammonia. —This is the most usual test for 
lime. 

9. Protochloride of Tin is a very powerful reducing 
agent, and is employed as a test for mercury and also for 
gold. 



SPECIAL BLOWPIPE REAGENTS. 


209 


10. Bichloride of Platinum is used for the detection of 
ammonia and potash. 

11. Perchloride of Gold is a test for the protosalts of tin. 

12. Zinc is principally employed for the reduction of 
antimony and tin. 

13. Copper is used for the reduction of mercurial salts 
and for the detection of arsenious acid. It also indicates 
the presence of nitric acid. 

14. Iron wire is employed to precipitate many metals, 
and in the separation of sulphur and the fixed acids from 
any substance with which they may be combined. The 
metals which can thus be precipitated, or deprived of 
sulphur, are copper, lead, nickel, and antimony. For 
instance, if a small piece of iron (harpsichord) wire be 
placed in a substance in fusion, and acted upon by the 
blowpipe, it becomes covered with the reduced metal. The 
latter sometimes appears as small globules. 

Iron has the property of reducing phosphorus from 
phosphoric acid or the phosphates, giving rise to a phos- 
phuret of iron, which forms on fusion a white, brittle, 
metallic globule. 

e. Special Reagents employed for determining the 

Presence of Acids. 

1. Acetate of Potash is used for precipitating phosphate 
of sesquioxide of iron from hydrochloric acid solutions of 
phosphates of the alkaline earths, and for precipitating 
from simple solutions in mineral acids substances insoluble 
in acetic acid. 

2. Hydrate of Lime , Lime Water. The former, hydrate 
of lime, is employed for the liberation of ammonia, and the 
latter for the detection of carbonic acid, oxalic acid, and 
tartaric acid, and lastly for indicating the presence of citric 
acid. 

3. Sulphate of Lime , for distinguishing and separating 
baryta and strontia. 

4. Sulphate of Magnesia , for the detection of phosphoric 
acid. 

i» 


‘210 


BLOWPIPE REAG ENTS. 


5. Chloride of Magnesium is used for the same purposes 
as sulphate of magnesia. 

0. Sulphate of Iron .—Used for indicating the presence 
of nitric acid ; and is also employed in solution for detecting 
hydroferrocyanic acid and for reducing the salts of gold. 

7. Neutral Acetate of Lead .—This is specially applied as 
a test for chromic acid and soluble chromates. 

8. Sidphate of Copper is used as a test for arsenious acid 
and arsenic acid. Also, for indicating the presence of 
hydroferrocyanic acid. 

9. Subnitrate of Mercury .—This reagent acts analogous 
to, and in many cases may be substituted for, nitrate of 
silver, in the detection of chlorine. 

10. Oxide of Mercury is used as a test for hydrocyanic 
acid. 

11. Chloride of Mercury is used as a test for hydriodic 
acid. 

12. Sulphurous Acid is a very powerful reducing agent. 
It precipitates metallic mercury from solutions of mercu¬ 
rial salts, reduces chromic acid to oxide of chromium, 
and is employed for the conversion of arsenic into arsenious 
acid. 

13. Chlorine is used in solution for isolating iodine and 
bromine. 

14. Sulphincligotic Acid is used as a test for nitric acid. 

15. Starch Paste is used as a test for iodine and bromine. 


II. REAGENTS IN THE DRY WAY. 

1. Carbonate of Soda. —The plain carbonate or the bi¬ 
carbonate may be indifferently employed ; but in either 
case it is absolutely necessary that it be free from sulphates. 
. There are two objects in view in the employment of soda 
as an auxiliary to the blowpipe ; firstly, to ascertain if the 
substances combining with this body be fusible or infusible; 
and secondly, to facilitate the reduction of certain metallic 
oxides. 

The Fusion of Substances with Soda. _Berzelius says, 


REAGENTS IX TIIE DllY WAY. 


211 


that w relatively to the employment of soda, there are many 
tilings to observe. The necessary quantity must be taken 
from its receptacle on the moistened point of a knife, and 
kneaded in the palm of the hand, so that it may form a 
coherent mass. If the body under examination be pulveru¬ 
lent it must be incorporated with it, but if in lump it must 
be placed upon it, forcing it slightly into the moistened 
soda ; then carefully heated on the charcoal with a gentle 
flame, until thoroughly dry; and lastly, it may be fused. 
It generally happens that the soda, at the instant of fusion, 
is absorbed by the charcoal; but this does not hinder its 
action on the assay; for if it be fusible with soda, the latter 
comes to the surface and attacks it, finally forming a liquid 
globule. If the substance be infusible in soda, but de- 
composible by it, it alters its appearance without entering 
into fusion. But, however, before pronouncing any 
substance to be infusible by soda, the flux ought to be 
mixed with the pulverised substance. If in these trials too 
little soda be taken, a portion of the substance remains solid, 
and the rest forms a covering of transparent glass; if too 
much, the bead of glass becomes opaque on cooling. It 
sometimes happens that the assay contains a substance which, 
being insoluble in the glass of soda, prevents it becoming 
transparent. Then, in order that we may fall into no error 
respecting the nature of the glass, it becomes necessary 
in the two last-mentioned cases to add a new quantity 
of the body under examination, and then ascertain if a 
limpid globule cannot be obtained. In general it is the 
best method to add the soda by successive small doses, and 
note the changes produced by each addition. It sometimes 
happens, in this kind of assay, that the glass becomes 
coloured at the moment of cooling, and finally takes a 
yellow or deep hyacinth red; it even becomes occasionally 
opaque and yellowish brown. These phenomena indicate 
the presence of sulphur, either in the assay or the soda 
employed. If the same colour be constantly produced by 
the same soda, it is a proof that it contains sulphate of 
soda ; it must then be discarded ; but if it gives generally a 


‘212 


REDUCTION BEFORE THE BLOWPIPE. 

colourless glass, it is the substance under assay that contains 
sulphur or sulphuric acid.’ 

Reduction of Metallic Oxides .—This species of assay, by 
which quantities of reducible metals, so small as to escape 
the best humid analyses, can be detected, is the most 
important discovery Gahn made in the application of the 
blowpipe. 

If a small quantity of native or artificial oxide of tin be 
placed on charcoal, it requires a long blast and a skilful 
operator to produce a grain of metallic tin; but if a small 
quantity of soda be added, the reduction takes place readily, 
and so completely with pure oxide, that the whole is trans¬ 
formed into a button of tin. From this it is certain, that 
the presence of soda favours the decomposition ; but in what 
manner ? Berzelius says that the reason is not known. 

The action, however, can be explained thus, as Berzelius 
himself hints : 4 The red-hot charcoal reacts upon the car¬ 
bonate of soda, producing by its reduction a certain amount 
of sodium, which by its strong attraction for oxygen seizes 
on that contained by the metallic oxide which is required to 
be reduced.’ If the metallic oxide contain an irreducible 
substance, the reduction of the former becomes difficult; but 
if a little borax be added, the reduction takes place as usual. 

This assay is very easy of execution, and the metal is 
moreover readily recognised, as by previous assays the nature 
of it is somewhat ascertained, and the reduction but confirms 
the previous idea. 

Supposing, however, that the metallic oxide be mixed 
with such a quantity of non-reducible substances that its 
nature cannot be ascertained by previous experiment, how 
can it be proved that a reducible metal is present P 

Gahn has solved this question in a very simple manner. 
4 After having pulverised the substance to be assayed, it 
is kneaded in the palm of the hand with moistened soda, 
and the mixture placed on charcoal and exposed to a good 
reducing flame; a little more soda is then added, and the 
blast recommenced. As long as any portion of the substance 
remains on the charcoal, soda is added in small portions, and 
the blast continued until the charcoal has absorbed the whole 


REDUCTION BEFORE TIIE BLOWPIPE. 


213 


of the mass. The first quantities of soda serve to collect 
the metallic particles scattered in the substance to be assayed, 
and the final absorption of the latter completes the reduction 
of any that may remain in the state of oxide. 

‘ This done, the burning charcoal is extinguished with a 
few drops of water; then having cut out the part which ab¬ 
sorbed the soda and assay, grind it to a very fine powder in 
an agate mortar. This powder is then washed with water to 
carry away the finest portion of the charcoal. The grinding 
and washing are repeated until all the charcoal is washed 
away. If the substance contained no metallic body, nothing 
will remain in the mortar after this last washing. But if it 
contained the smallest quantity of reducible matter, it is 
found at the bottom of the mortar, as small brilliant plates if 
it be malleable, or as a fine powder if it be brittle or not 
fusible. In either case, the bottom of the mortar is covered 
by metallic traces, resulting from the friction of the particles 
of metal against its sides, (provided that the quantity of metal 
contained in the sample be not too small). The flattening 
of almost imperceptible globules of any malleable metal 
converts them into shining discs of a perceptible diameter. 
In this manner may be discovered by the blowpipe, in an 
assay of ordinary size, less than a half per cent, of tin, and 
even less than that of copper. ’ 

The following points in this class of assay ought to be 
particularly attended to. Firstly, to produce the strongest 
possible flame, taking care that it covers every part of the 
assay. Secondly, to leave none of the metal in the charcoal, 
or lose the smallest quantity in the collection. Thirdly, to 
well grind the carbonaceous mass. Fourthly, to decant 
very slowly, so that only the lighter parts may be carried 
away by the water. Fifthly, not to judge of the result 
until the wdiole of the charcoal has been removed, for a 
small quantity remaining suffices to hide the metallic 
particles; and, moreover, the particles of charcoal, viewed 
in a certain light, have themselves a metallic lustre, which 
will deceive an inexperienced eye. Sixthly and lastly, not 
to trust to the naked eye, however plain the sample may be, 
but always examine by the aid of a good microscope. 


214 


EORAX. 


The metals reducible by this process are (besides the noble 
metals), molybdenum, tungsten, antimony, tellurium, bis¬ 
muth, tin, lead, copper, nickel, cobalt, and iron. Amongst 
these, antimony, bismuth, and tellurium volatilise easily when 
they are exposed to a strong heat. Selenium, arsenic, cad¬ 
mium, zinc, and mercury volatilise so completely that they 
cannot be collected except by means of a small subliming 
apparatus. 

The reduction can always be effected the first time when 
the assay contains from 8 to 10 per cent, of metal; but in 
proportion as the standard decreases more attention and 
care must be paid to the washing and recognition of the 
reduced metal in the mortar. A good system of practice in 
this experiment is to employ any cupreous substance, and 
make on it a great number of experiments, taking care to 
mix it each time with a substance containing no copper ; thus 
the metallic value will diminish at each new assay, until at 
last no copper can be found. 

If the substance to be assayed contains several metals, the 
reduction of their oxides must be made in globo , and a 
metallic alloy obtained. Some, small in number, are reduced 
separately. For instance, copper and iron give a regulus of 
each metal; copper and zinc, the first gives a regulus of 
copper, whilst the latter volatilises. But when the resul t of the 
operation is an alloy, recourse must be had to the reactions 
produced by other fluxes to ascertain its constituents. 

2. Borax (Biborate of Soda). —The borax of commerce 
must be dissolved in hot water and recrystallised, before it 
can be used in blowpipe analysis. Gahn made many ex¬ 
periments on the fusion of borax on charcoal with soda, until 
both salts were absorbed; a whitish metal was produced, 
which appeared to proceed from the vessels in which the 
borax was manufactured. This never happened with borax 
which had been recrystallised. 

Borax may be employed either in crystals, the requisite 
size for an assay, or in a pulverulent form ; in this case it 
may be taken up on the moistened point of a knife. Some 
operators prefer fusing the borax before use, in order to 
drive off its water of crystallisation, and thus avoid the 


FUSION WITH BORAX. 


215 


tumefaction ensuing after the heating of a crystal on charcoal. 
This, as Berzelius observes, would be an excellent precau¬ 
tion, provided the borax did not regain its water of crystal¬ 
lisation, but it recovers it to a small extent, and boils up 
when exposed to the blowpipe flame, although not so 
much as before ; the tumefaction is, however, no great incon¬ 
venience, and it is not difficult to fuse a mass so tumefied 
into a globule. 

Borax is employed in the solution or fusion of a variety of 
substances. It is best to commence by acting upon a scale 
of the substance to be examined; because if a powder be 
employed the resulting action cannot be so well ascertained. 
The following phenomena are to be carefully watched, for 
in treating any substance with borax it must be particularly 
noted whether the fusion takes place rapidly or otherwise ; 
without motion or with effervescence ; if the glass resulting 
from the fusion is coloured, and if that colour changes in 
the oxidising or reducing flame ; and lastly, if the colour 
diminishes or increases on cooling, and if, under the same 
circumstances, it loses or retains its transparency. 

Some substances possess the property of forming a limpid 
glass with borax, which preserves its transparency on cooling, 
but which, if slightly heated in the exterior (oxidising) flame, 
becomes opaque and milk-white, or coloured when the flame 
strikes it in an unequal or intermittent manner. The alkaline 
earths, as yttria, giucina, zirconia ; the oxides of cerium, 
tantalum, titanium, &c., belong to this class. In order to be 
certain of this result we must assure ourselves that the glass 
is saturated to a certain point with either of the above class of 
bodies. The same thing, however, does not happen with 
silica, alumina, the oxides of iron, manganese, &c., and the 
presence of silica prevents the production of this phenomenon 
with the earths; so that alone they present this peculiar 
appearance witli borax ; but when combined with silica (as 
natural silicates, for instance,) no such effect is produced. 
This operation has received the name of flaming , and any 
substance thus acted upon is said to become opaque by 
flaming. 

3. AmmoniO'Phosphate op Soda (Microcosmic Salt) is ob- 


21G 


FUSION WITH MICROCOSMIC SALT. 


tained by dissolving 1G parts of sal-ammoniac in a very small 
quantity of boiling water, and mixing with it 100 parts of 
crystallised phosphate of soda, dissolving the whole witli 
heat, filtering the boiling liquid ; during cooling the double 
salt crystallises. When microcosmic salt is not pure it 
forms a glass which becomes opaque by cooling. It is then 
necessary to dissolve it in a small quantity of water and 
recrystallise it. 

It may be collected in large crystals, or in a pulverulent 
state. The crystals are in general of a suitable size for 
ordinary assays. Placed on charcoal, and submitted to the 
blowpipe flame, it bubbles and swells up, giving off am¬ 
monia ; that which remains after this treatment is an acid 
phosphate of soda, which fuses readily, and forms on cooling 
a transparent and colourless glass. As a reagent, it acts 
principally by its free phosphoric acid ; and if the salt be 
employed in preference to the acid, it is because it is less 
deliquescent, costs less, and passes readily into the charcoal. 
By means of microcosmic salt we then ascertain the action 
of free acids on any substance we may wish to assay. The 
excess of acid it contains combines with all bases, and forms 
a class of double salts, more or less fusible, which are exa¬ 
mined as to their transparency and colour. In consequence, 
this flux is used more particularly in the detection of the 
metallic oxides, most of which impart to it very charac¬ 
teristic colours. This flux exercises on acids a repulsive 
action. Those which are volatile, sublime ; and those which 
are fixed remain in the mass, dividing the base with the 
phosphoric acid, or yielding it up entirely ; in which case they 
are suspended in the glass without being dissolved. In this 
respect, microcosmic salt is a good test for silicates ; for by 
its aid silica is liberated, and appears in the glass as a 
gelatinous mass. 

4. Nitrate of Potash (Nitre), in long and thin crystals, is 
employed in hastening the oxidation of those substances 
which do not readily combine with oxygen in the exterior 
flame. It is used as follows: the point of a crystal is thrust 
into the fused bead ; but in order to prevent the cooling 
of the latter the crystal is held by a pair of pliers, so that 


FUSION WITH B1SULPIIATES. 


917 


when the bead begins to cool it may be withdrawn, the 
head reheated, and the crystal employed as before, until 
the desired effect is produced. 

5. Bisulphate of Potash is employed in the detection of 
lithia, boracic acid, nitric acid, hydrofluoric acid, bromine, 
and iodine. It separates baryta and strontia from the earths 
and metallic oxides. 

Professor J. Lawrence Smith* lias suggested the use of 
bisulphate of soda as a substitute for the bisulphate of potash 
in the decomposition of minerals, especially the aluminous 
minerals. He says that 4 bisulphate of potash is still used, to 
the almost utter exclusion of bisulphate of soda in rendering 
certain minerals soluble; and it is still recommended as the 
proper agent to fuse with aluminous minerals, as corundum, 
emery, &c. 

4 This subject occupied my attention to a considerable 
extent when engaged in the preparation of two memoirs 
on the geology and mineralogy of emery, presented to 
the French Academy of Sciences in 1850, as well as in 
some investigations I am now making on the emery from 
Chester, Massachusetts. In the above researches I had a large 
number of corundums and emeries to analyse. The powxlered 
minerals were fused with the bisulphate of potash in the 
usual way, and I found no difficulty in decomposing the 
minerals ; but unfortunately during the operation a double 
salt of potash and alumina is formed, which is almost 
insoluble in the water or in the acids; and it is only by a 
solution of potash that it is first decomposed and afterwards 
redissolved. There are many disadvantages and delays 
attendant upon this method, which experience soon exhibits ; 
as the constant deposition of alum, if the solution is not 
kept quite dilute. I therefore experimented with the bisul¬ 
phate of soda, knowing that the double salt of alumina and 
soda was quite soluble, and my results were everything that 
could be desired ; for while the soda salt gives a decompo¬ 
sition at least as complete as the potash salt, the melted mass 
is very soluble in water, and in the future operations of the 
analyses there is no embarrassment from a deposit of alum. 

* American Journal of Science and Arts. 


218 


BLOWPIPE TESTS AND REAGENTS. 


c The ordinary commercial article is not sufficiently pure 
for use, and I prepare it from pure carbonate of soda or 
sulphate of soda that has been purified by recrystallisation. 
In either instance pure sulphuric acid is added in excess to 
the salt in a large platinum capsule, and heated over a flame, 
until the melted mass, when taken up on the end of a glass 
rod, solidifies quite firmly. The mass is then allowed to 
cool; moving it over the sides of the capsule will facilitate 
this operation. When cool it is readily detached from the 
capsule, is then broken up, and put into a glass stoppered 
bottle. So far as my experience has yet gone, in almost every 
instance where we have been in the habit of using bisul¬ 
phate of potash the bisulphate of soda can be substituted.’ 

G. Vitrified Boracic Acid is used to ascertain the presence 
of phosphoric acid and small portions of copper in lead alloys. 
For quantitative analysis, it is generally used to ascertain 
the quantity of copper contained in a lead ore, and also 
the amount of copper united with various metals. 

7. Nitrate of Cobalt in solution ought to be free from 
arsenic and nickel, and the solution must be moderately 
strong. It is used as a test for alumina, magnesia, tin, and 
zinc, by the blowpipe. 

8. Oxalate of Nickel is used in qualitative examinations 
for the detection of potash in a salt which also contains soda 
and lithia. 

9. Oxide of Copper is employed to detect the presence 
of hydrochloric acid and chlorine. 

10. Silica is,'with soda, an excellent test for the presence 
of sulphuric acid ; and when in combination with borax or 
soda, separates tin from copper. 

11. 12. Fluoride of Calcium (Fluor-spar), and Sulphate 
of Lime (Gypsum). —These two bodies (deprived of water) 
are used to indicate the presence of each other. If a small 
piece of gypsum be ignited in contact with a similar piece 
of fluor-spar, they soon liquefy at their points of contact; 
they then combine, and form, by fusing, a colourless and 
transparent bead of glass, which becomes enamel-white on 
cooling. Fluoride of calcium is thus employed as a test for 
gypsum, and vice versd. 



BONE ASII, LEAD, TINFOIL. 


219 


It serves, also, when mixed with bisulphate of potash, to 
detect lithia and boraeic acid in their various combinations. 

13. Bone Ashes are employed in the cupellation of gold 
and silver. Harkort reduced them to many states of 
minute division by the processes of sifting and washing. 
The bones are burned until they become perfectly white, 
and then freed from any carbonaceous matter that may 
have adhered to them. This being done, they are pulverised 
in a mortar, and the finer portions separated by a sieve. 
The remaining powder is then thrown upon a filter, and 
treated with boiling water, which extracts the soluble matter. 
The washing, which is then resorted to, is for procuring 
the bone ashes of a more uniform degree of fineness. The 
mass from the filter is mixed with water in a cylindrical 
glass, allowed to settle for a few minutes and then decanted ; 
the coarser powder is deposited at the bottom of the 
vessel, while the finer passes over, suspended in the water. 
By repeated decantations in this way, deposits are obtained 
of different degrees of fineness ; the last, or that which remains 
longest floating through the liquid, being the finest. The 
resulting powders must be kept in separate bottles. The 
coarser ashes are used for cupellation of rich silver ores, 
and the finer for assaying ores in which only a minute 
quantity of gold or silver is present. 

14. Proof Lead is made use of in cupelling argentiferous 
or auriferous substances ; it must be free from silver. Dumas 
states that the best method of obtaining lead in this desirable 
state is to decompose the best white-lead by means of 
charcoal, as it is then impossible for it to contain any other 
metal. 

15. Tinfoil is employed to reduce certain peroxides 
to the state of protoxide. When it is used, a small roll, 
about ^ of an inch long, is plunged into the fused button, 
and heated strongly in the reducing flame : the desired effect 
is then produced. 

1G. Dry Chloride of Silver. —Herr H. Gericke proposes 
the employment of this compound in qualitative blowpipe 
assays. In an elaborate paper on this subject, communicated 
to the Chemical Gazette (vol. xiii. p. 189) he says:— 


220 


USE OF CHLORIDE OF SILVER 


4 Amongst the phenomena which characterise different 
bodies before the blowpipe, and serve for their distinction, 
the colour of the flame is of no small importance. This 
power of colouring the blowpipe flame is not, however, 
exhibited by all bodies with sufficient intensity to enable 
them to be distinguished by it with certainty ; and certain 
substances are consequently usually employed, such as mu¬ 
riatic acid with baryta, strontia and lime, or sulphuric acid, 
partly to form and partly to set free volatile compounds. 
By this means, however, although the intensity of the 
coloration is heightened, its duration is not increased, as 
these acids, and particularly muriatic acid, evaporate for the 
most part before they have acted sufficiently, so that the color¬ 
ation lasts only for a few moments. This defect may be got 
over by the employment, instead of the volatile muriatic 
acid, of a chloride, which will retain the chlorine at a high 
temperature, so that it may only be set free by degrees in 
small quantities, while the body forming its base may be 
without action upon the colouring power of the body under 
investigation. For this purpose chloride of silver appears 
to be the best, especially as it may readily be prepared in 
a state of purity. The best plan is to stir it with water into 
a thick paste, and keep it in a bottle. 

4 In regard to the action of chloride of silver upon the 
coloration of the blowpipe flame, I have investigated 
several compounds of potash, soda, lithia, lime, baryta, 
strontia, copper, molydenum, arsenic, antimony, and lead, 
and mixtures of these substances. Chloride of silver, of 
course, has no action upon borates and phosphates, both of 
these acids being amongst those which offer the most resist¬ 
ance to the action of heat. 

4 For a support, I employed first of all platinum wire, but 
this is soon alloyed by the metallic silver which separates, 
and thus rendered useless in testing metals. Silver wire 
is too readily fusible, and also difficult to obtain free from 
copper, which may give rise to errors when in contact with 
chloride of silver. For these reasons, iron wire is best 
fitted for experiments with chloride of silver, as from its 
cheapness a new piece may be employed for each experi- 


IX BLOWPIPE ASSAYS. 


221 


ment, while the silver may readily be obtained in the form 
of chloride from the broken pieces. If the size of the frag¬ 
ment under examination be sufficient, the platinum forceps 
may be employed. 

4 J he results at which I arrived, by the employment of 
chloride of silver, in comparison with those obtained without 
this reagent, are as follows : 

4 With potash compounds, such as saltpetre, potashes, Ac., 
the flame is decidedly of a darker colour with chloride of 
silver; and even in ferrocyanide of potassium, which, when 
treated by itself with the blowpipe, colours the dame blue, 
the addition of chloride of silver produces a distinct potasli 
coloration. 

4 The action of chloride of silver upon soda salts is not so 
favourable; for although with some, as nitrate of soda, 
common soda, and labradorite, the flame acquires a more 
intense yellow colour by the addition of chloride of silver, 
this reagent produces no observable difference with other 
soda compounds, such as sulphate of soda and analcime. 
This also applies to the compounds of lithia, some of which 
give a finer purple-red colour on the addition of chloride of 
silver, whilst upon others it has no such effect. 

4 With lime compounds chloride of silver acts favourably 
upon the colouring power. Thus the addition of chloride 
of silver to calcareous spar or gypsum (in the reduction 
flame) gives the flame a more distinct yellowish-red colour, 
but stilbite gives no coloration either with or without 
chloride of silver. With fluor-spar the coloration cannot 
well be observed, as this decrepitates too violently under 
the blowpipe. 

4 The action of chloride of silver upon compounds of 
baryta and strontia is decidedly advantageous, as both the 
intensity of the coloration and its duration leave nothing 
to be desired. Siliceous celestine, which, when heated by 
itself in the forceps, scarcely coloured the flame, immediately 
produced a permanent red coloration when heated with 
chloride of silver. 

4 Although it appears from the preceding statements, that 
the employment of chloride of silver presents no advantage 


222 


USE OF CIILOKIDE OF SILVER 


with some substances, it may be used with good results in 
the treatment of mixtures of alkalies and earths. 

k Thus, with petalite alone, the litliia coloration is first 
produced, and a slight soda coloration is afterwards 
obtained : whilst with chloride of silver the soda coloration 
appears very distinctly after that of the litliia. With lithion 
mica alone a very distinct litliia coloration is presented; 
but in the presence of chloride of silver a colour is first pro¬ 
duced which may lead to the conclusion that potash is 
present, but the litliia coloration is weakened. Ryacolite , 
heated by itself in the blowpipe flame, only gives a distinct 
soda coloration ; but with chloride of silver a slight potash 
coloration is first produced, and the colour of soda then 
appears very distinctly; the lime contained in it cannot 
however be detected by the coloration of the flame. 

4 Chloride of silver may be employed with still greater ad¬ 
vantage with the following metals, but in these cases it is par¬ 
ticularly necessary that the operator should become familiar 
with the colour produced by each individual substance. 

4 With copper compounds, such as red copper ore, mala¬ 
chite, copper pyrites, sulphate of copper &c., when contained 
in other minerals so as to be unrecognisable by the eye, 
the employment of chloride of silver may be of the greatest 
service, as the smallest quantities of copper, when treated 
with chloride of silver under the blowpipe, give a continuous 
and beautiful blue colour to the flame. With chloride of silver 
the presence of copper may be distinctly ascertained by the 
blowpipe, even in a solution which is no longer coloured 
blue by the addition of ammonia. 

4 The employment of chloride of silver will be equally 
advantageous with molybdenum, as in this case also the 
flame gains greatly in intensity. Arsenic, lead, and anti¬ 
mony are already sufficiently characterised, the former by 
its odour, the two latter by their fumes ; but even with 
these metals chloride of silver may be employed with advan¬ 
tage to render their reactions still more distinct. It is only 
necessary to observe, that the greenish-blue flame of anti¬ 
mony appears greener and more like that of molybdenum 
under the influence of chloride of silver. 


IN BLOWPIPE ASSAYS. 


223 


4 Chloride of silver may also be employed with compounds 
containing several of the above-mentioned metals. 

4 If boumonite be heated in the oxidation flame of the blow¬ 
pipe, a fine blue flame is first produced, which indicates 
lead with certainty ; if chloride of silver be now applied, 
copper is also readily shown. The antimony contained in 
boumonite cannot be ascertained by the coloration of the 
flame ; but this may easily be detected upon charcoal, or in 
a glass tube open at both ends. 

4 Native molybdate of lead, without chloride of silver, only 
gives a blue colour to the blowpipe flame ; with chloride of 
silver this blue coloration of the lead comes out more dis¬ 
tinctly, but at the same time the tip of the flame, particu¬ 
larly when the reduction flame is employed, appears of a 
beautiful yellowish-green colour from molybdenum. 

4 With mixtures of arsenic and copper, or antimony and 
copper, the flame first acquires a greyish-blue or greenish- 
blue colour from the oxidation of the arsenic or antimony; 
the copper may then be very easily detected by chloride of 
silver. This applies also to mixtures of arsenic and molyb¬ 
denum, or antimony and molybdenum; with chloride of 
silver the yellowish-green flame of molybdenum appears dis¬ 
tinctly. It will be more difficult to analyse mixtures of 
arsenic and lead, or antimony and lead, in this manner ; 
and if a compound contain both arsenic and antimony, these 
two bodies are not to be distinguished with chloride of 
silver under the blowpipe. 

4 From these experiments it appears that in blowpipe test¬ 
ing, it is more advantageous to employ chloride of silver, 
instead of muriatic acid. 

4 Chloride of silver is particularly to be recommended in 
testing metallic alloys for copper. Thus, to test silver for 
copper, chloride of silver may be applied to the ends of 
silver wires, and on the application of heat the smallest 
quantity of copper will furnish the most distinct reaction. 
This is as sensitive as any of the known copper reactions, and 
may be performed quickly and easily. In testing metallic 
alloys for traces of copper, it may be advisable to submit 
those which contain antimony, zinc, lead, and other volatile 


224 


SODA PAPER. 


metals to roasting, so as to drive off these metals before 
the addition of chloride of silver.’ 

GENERAL ROUTINE OF BLOWPIPE OPERATIONS. 

Size of the Assay .—The morsel operated on is sufficiently 
large when the effect of the heat and the fluxes added can 
be distinctly discerned. The size of the assay-piece gene¬ 
rally recommended is much too large; its size ought to be 
about that of a mustard-seed ; that of the flux added, 
about the size of a hemp-seed. It should in general be 
previously reduced to fine powder. 

Soda-Paper. —Mr. Forbes writes as follows in the Chemi¬ 
cal News ‘ As it would be impossible to submit any pow¬ 
dered substance to the direct action of the blowpipe flame 
without its suffering mechanical loss, some means must be 
employed for holding the particles together until they are 
so agglutinated by the heat that no such loss need be appre¬ 
hended ; this is secured by the use of the soda-paper en¬ 
velope or cornet, as devised by Harkort. For this purpose 
slips of thin slightly sized writing paper, about 1^ inch long 

by 1 inch broad, are steeped 
in a solution of one part cry¬ 
stallised pure carbonate of soda 
(free from sulphate) in two 
parts of water. When dried 
these are used for forming 

o 

small cylindrical cornets, by 
rolling them round the ivory 
cylinder, fig. 70 cZ, previously 
described. A hollow is formed 
to them by folding down a por¬ 
tion of their length on to the end 
of the cylinder, which is then 
pressed firmly into the corre¬ 
sponding mould in the blowpipe anvil, and which, upon 
the withdrawal of the cylinder, serves as a support until they 
are filled with the assay from the scoop in which the assay 
and flux have been mixed. After pressing the assay down, 




































OPERATIONS IN BLOWPIPE ANALYSIS. 


225 


the superfluous paper is cut off, leaving only sufficient when 
folded down upon the contents of the cornet, to form a paper 
cover to the top similar to the hollow of the cornet. 
The assay is then ready for placing in a bore in the char¬ 
coal, formed by the charcoal borer c, fig. 68, and is then 
submitted to a reducing fusion.’ 

When a large piece is employed, the experiment consumes 
so much more time and requires so much more labour than 
a smaller piece. It is only in reductions that a larger piece 
may be successfully employed, because in that case the 
more metal produced, the more readily can its nature be 
ascertained. Having thus endeavoured to fix the size of 
the assay, we will now lead our readers to the operations 
necessary in blowpipe analysis, and in the order in which 
they are to be performed. 

Firstly .—The substance is heated in the closed tube, or 
matrass, over a spirit-lamp. It may, by this treatment, 
decrepitate, or give off water, or some other volatile sub¬ 
stance. 

Secondly .—It is heated gently on charcoal, by aid of the 
blowpipe; and, as soon as warm, withdrawn from the 
heat, and the odour given off ascertained : volatile acids, 
arsenic, selenium, or sulphur, may be present. The odour 
thus produced by the oxidising flame must be compared 
with that produced by the reducing flame ; if any differ¬ 
ence, it must be carefully noted. Sulphur, selenium, &c., 
are best detected in the oxidising flame, and arsenic in the 
reducing flame. 

Thirdly .—The substance is examined as regards its fusi¬ 
bility. If it be in grains, it is better acted upon on charcoal, 
notwithstanding its liability to escape on the first insuffla¬ 
tion, when not very fusible. But if we can choose the 
form, it is better to knock off a small splinter, by means of 
the hammer, and hold it in the flame by the platinum- 
pointed pincers. A fragment with the most pointed and 
the thinnest edges ought to be selected. By thus acting, 
we can always ascertain at a glance if the substance be 
fusible or not. Infusible substances retain their sharp 
points and angles, which can be ascertained immediately by 

Q 


22(5 


FUSIBILITY OF MINERALS. 


means of a microscope. The points are merely rounded 
in bodies of difficult fusibility, and in substances of easy 
fusion are rendered globular. 

Certain substances, and particularly some minerals, change 
both aspect and form when exposed to the blowpipe flame, 
without entering into fusion; some swell up like borax ; 
some of them fuse after tumefaction ; others keep in that 
state without fusion. Some minerals give off a sort of foam 
on fusing, giving rise to a kind of blebby glass, which, 
although transparent itself, does not appear so, on account 
of the multitude of air-bubbles it contains. 

This bubbling and tumefaction take place in the greater 
part of the minerals only at that temperature at which all 
the water is disengaged ; and these ramifications appear to 
proceed from a new molecular arrangement, produced by 
the action of heat on the constituent parts of the sub¬ 
stance. It cannot be said that the expansion of a particular 
part of the substance, or its formation into gas, gives rise to 
this, because it most often happens in those substances which 
contain no such substance. The minerals which generally 
give these indications are the double silicates of lime, or 
alkali and alumina. It sometimes disappears after a few 
instants, and occasionally lasts as long as the substance is 
kept in fusion. In the latter case, it seems that the assay 
takes carbonic acid from the flame, which carbonic acid is 
transformed by the charcoal into carbonic oxide, and it is 
that gas which causes the bubbles. 

The examination of the comparative fusibility of minerals 
is of essential importance, as many which consist principally 
of earths, and contain very little of true metallic oxides, can 
readily be distinguished by this means. Hence it is that 
the list given by Bose, of a considerable number of minerals 
arranged according to their different degrees of fusibility, is 
of great interest. 

Of the minerals which occur most frequently, the following 
are, when heated between the platinum-points of a forceps 
in a strong flame, perfectly infusible: Quartz , Corundum , 
Spinel, Zeylanite , Pleonaste , Automolite , Gahnite , Olivine , 
Cerite , Zircon , Disthene , Cyanite , Leucite , Talc, Gehlenite , 


EMPLOYMENT OF FLUXES. 


227 


Anthopliylhte, Staurelite, Allophane, Kymopliane, Gado- 
linite. 

The following phosphoresce on being heated: Rutile 
Titaneisen, Tantalite, Turquoise, Calaite, Chondrodite, 
Topaz. 

The following are fusible with difficulty, or only on the 
edges : Adularite, Tetartine, Albite, Petalite, Labradorite, 
Anorthite, Tabular Spar, Meerschaum, Speckstein, Serpentine, 
Epidote. 

The following tumefy on the first application of heat: 
Dichroite (some varieties moderately fusible), Beryl , Emerald, 
Euclase, Titanite, Sodalite, Schwerstein, Tungstate of Lime, 
Heavy Spar, Sulphate of Baryta, Celestine, Gypsum, Apatite, 
Fluor-spar. 

Amongst fusible minerals are the Zeolites, most of which 
present intumescence when heat is first applied, Oligo- 
clase, Soda Spodumene, Spodumene, which also tumefies, 
Meionite, Elaolite, Nepheline. Amphibolite, the greater 
part of which effervesce during fusion. The Pyroxenes, of 
which those containing large quantities of magnesia are 
with difficulty fusible, Vesuvian, Idocrase, which tumefies 
on melting, Orthite, which boils while fusing, Wolfram, 
Boracite, Datholite, Botryolite, Tourmaline and Axinite, 
which swell up when melted, Amblygonite, Lazurstein, 
llauyn, Nosin, Eudyalite, and Pyrosmalite. 

In the employment of fluxes, it is necessary to continue 
the blast for a sufficiently long time, because some sub¬ 
stances appear infusible at the commencement of the opera¬ 
tion, and gradually yield to the influence of the flux, and in 
about two minutes enter into full fusion. The substance is 
best added in small quantities, and no new dose must be 
introduced until the former one is perfectly acted upon, so 
that at last the glass arrives at that degree of saturation 
that it can dissolve no more: it is at this particular point 
the reactions are most vivid and plain. Beads of glass, not 
so saturated, do not give such decided indications. 

Occasionally, in operating with a flux in the reducing 
flame, it happens that the assay-bead reoxidises during the 
cooling of the charcoal, and thus the labour of a preceding 


228 


BLOWPIPE REACTIONS. 


operation is lost. In order to obviate this inconvenience, 
the charcoal is turned over, so that the bead may fall in a 
yet liquid state on some cold body, as a porcelain plate. 

When the colour of the bead is so intense that it appears 
opaque, its transparency can be proved by holding it oppo¬ 
site to the flame of a lamp ; the reversed image of the llame 
can then be seen in the bead, tinged with the colour im¬ 
parted to the flux by the body under experiment. The 
globule may also be flattened by a pair of pliers before it 
cools, or it may be drawn into a thin thread. In either of 
the last-mentioned cases its colour can readily be ascertained. 

Minerals exposed to the exterior and interior flame, either 
with or without fluxes, present a variety of phenomena, 
which ought to be carefully noted, and which, collectively, 
form the result of the assay. The smallest circumstance 
must not be overlooked, because it may lead us to ascertain 
the presence of a substance not suspected. It is necessary, 
in all cases, to make two assays, and compare the separate 
results; because it sometimes happens that an apparently 
trivial fact had been overlooked in the first series of opera¬ 
tions, which materially conduces to the good result of the 
experiment. 

Potash, Soda, and Lithia cannot be distinguished with any 
degree of certainty by the blowpipe ; their presence is best 
ascertained by the wet assay ; that is to say, however, with 
the exception of soda. Potash colours the blowpipe flame 
bluish ; soda, yellow; and lithia, red. These indications, 
however, will be more fully discussed under the head of 
Coloured Flames. 

Baryta, alone, is infusible. The hydrate is fusible, but 
soon becomes a solid crust, on account of its losing water. 

Carbonate of Baryta (BaO,C0 2 ) fuses very readily into a 
limpid glass; and, on cooling, takes the appearance of a 
white enamel. On charcoal it effervesces, and becomes 
caustic baryta ; it then behaves as above stated. 

With borax , baryta fuses easily into a limpid glass, with 
a lively effervescence. It becomes opaque by flaming . 

With microcosmic salt it fuses easily, with a brisk effer- 


BLOWPIFE REACTIONS. 


229 


vescence, during which the globule foams and swells; after 
which it is transformed into a limpid glass. 

With soda it fuses and sinks into the charcoal. 

With nitrate of cobalt it produces a bead, which, when 
hot, is brick-red. It loses this colour by cooling. 

Strontia. — Alone , it presents the same phenomena as 
baryta; as it does also with microcosmic salt and borax. 

Soda does not dissolve caustic strontia. Carbonate of 
strontia, mixed with its own volume of soda, fuses into a 
limpid glass, which becomes enamel-white on cooling. 

With nitrate of cobalt strontia becomes black, or greyish- 
black, and does not fuse like baryta. 

Lime, alone, undergoes no alteration. Carbonate of lime 
becomes caustic, giving off a very strong light. 

With borax it readily fuses, giving a limpid glass, which 
becomes opaque by flaming. 

With microcosmic salt it fuses in large quantity, giving rise 
to a limpid glass, which preserves its transparency on cooling. 

Soda scarcely acts either upon lime or its carbonate, 
passing into the charcoal, and leaving them unaltered upon 
its surface. 

Acted on by nitrate of cobalt , lime gives a blackish mass, 
which is infusible. 

Magnesia, alone , undergoes no alteration. 

With borax , behaves as with lime. 

With microcosmic salt , fuses readily. 

With soda , no action. 

With nitrate of cobalt , after a strong heat, becomes flesh- 
red ; which tint, however, is not well seen until after perfect 
cooling. 

Alumina, alone , does not change. 

With borax , fuses slowly, and forms a diaphanous glass, 
which becomes opaque either by cooling or flaming. 

With microcosmic salt , it forms a transparent glass. 

With soda it swells a little, forming an infusible compound. 
The excess of soda is absorbed by the charcoal. 

With nitrate of cobalt it gives a fine blue colour by a 
strong blast. This colour is best observed by daylight, and 
is very characteristic of alumina. 


230 


BLOWPIPE REACTIONS. 


Molybdic Acid. — Alone, in the open inclined tube, it fuses, 
giving off a white smoke, which condenses in the form ot a 
white powder on the sides of the tube. Heated on platinum 
foil, it fuses and smokes. The fused portion is brown, but 
becomes yellowish and crystalline on cooling. In the re¬ 
ducing flame it becomes blue. 

With borax it fuses on the platinum wire, forming in the 
exterior flame a colourless and transparent glass. On char¬ 
coal, in the reducing flame, the glass becomes brown, and 
loses its transparency. 

With microcosmic salt it fuses on the platinum wire in 
the exterior flame, producing a transparent glass, which, 
while hot, is greenish, but which colour it loses on cooling. 
In the reducing flame, the green becomes opaque, and appears 
black or deep blue, but by cooling becomes nearly as beau¬ 
tiful a green as that produced by oxide of chromium. 

With soda , molybdic acid fuses on the platinum wire 
with effervescence, forming a limpid glass, which becomes 
milk-white by cooling. 

Acted on by soda on charcoal, molybdic acid is absorbed 
as soon as fused ; and by removing the charcoal which has 
absorbed it, and treating it by washing and grinding, 
metallic molybdeum may be obtained. 

Tungstic Acid. — Alone , it blackens, but does not fuse in 
the reducing flame. 

With borax it fuses readily on the platinum wire, forming 
a colourless glass in the outer flame, which does not become 
opaque by flaming. In the reducing llame the glass is 
yellowish when it contains only a small proportion of acid, 
and the colour augments in intensity by cooling, becoming 
perfectly yellow. 

With microcosmic salt , tungstic acid dissolves, forming 
in the exterior flame a colourless or slightly yellowish 
glass. In the reducing flame it becomes a fine blue, more 
beautiful than that of cobalt. If the acid contains iron, the 
glass assumes a perfectly different appearance, becoming 
blood-red. 

Soda dissolves tungstic acid on the platinum wire, con¬ 
verting it into a transparent and dee}) yellow glass, which 


BLOWPIPE REACTIONS. 


231 


crystallises on cooling, becoming an opaque white or 
yellow. If tungstic acid be treated on charcoal with a 
small quantity of soda in the reducing flame, a steel-grey 
slag is obtained, which, by washing and levigating, furnishes 
metallic tungsten. 

The reactions produced on the various compounds of the 
commoner metals, by the blowpipe, with and without fluxes, 
will be given under their respective headings. 

Silica. — Alone , undergoes no change, 

With borax it fuses slowly and gives a clear glass, of 
difficult fusion, which is not rendered opaque by flaming. 

Microcosmic salt dissolves but a very small quantity. The 
fused glass preserves its transparency after cooling ; that 
which is half fused has but a semitransparency. 

With socla it fuses, giving rise to brisk effervescence, with 
the production of a limpid glass. 

With solution of cobalt , in certain proportions, it takes a 
faint bluish tint, which becomes black, or deep grey, ac¬ 
cording to the quantity of cobalt. It is by means of this 
colour that silica is distinguished from some aluminous 
substances. 

Sulphur gives, on burning, the well-known odour which 
is due to the formation of sulphurous acid. It leaves no 
residue, when pure, on being heated on platinum foil. 

Compounds of Sulphur with the Metals : Sulphides. —These 
bodies may be recognised by the odour of sulphurous acid 
they exhale when heated on charcoal or in the open tube. 
When the quantity of sulphur contained in any compound 
is too small to be detected by the smell, its presence may 
be ascertained by fusing it with a bead composed of car¬ 
bonate of soda and silica. The glass, on cooling, takes a 
brown or reddish-yellow colour, according to the quantity 
of contained sulphur. This method cannot always be 
employed, because the associated metals mask the colour ; 
in this case the mineral must be roasted in the open 
tube, in the upper part of which is placed a piece of Brazil¬ 
wood paper. If sulphur be present, the red colour of the 
paper will disappear. A quantity of sulphur so small as to 




232 


BLOWPIPE REACTIONS. 


be imperceptible to the smell, will bleach this test-paper. 
This method must always be followed in the detection of 
sulphur in the sulphides of antimony, because it is difficult 

to ascertain its presence by the smell. 

The principal object, however, in view in the examination 
of the metallic sulphides, is to ascertain the presence of 
some particular metal, in which case they must be roasted, 
taking care to observe the precautions pointed out for the 
roasting of ores for assay by the furnace. The roasting 
must always be executed in the oxidising flame, and great 
care taken to apply only a very gentle heat at first, other¬ 
wise the assay will fuse, and it will then be impossible to 
continue the roasting with the sample. Great care must be 
taken to expel the whole of the sulphur, otherwise no re¬ 
duced metal can be obtained by the action of soda, as 
sulphide of sodium forms fusible compounds with most of 
the metallic sulphides. 

Selenium can be sublimed under the same circumstances 
as sulphur. The sublimate, if small, is reddish; but if large, is 
of so deep a colour as to appear black. It gives, when heated 
in the open air, a strong smell of decayed horseradish. 
Owing to this peculiar smell, it is very readily distinguished 
by the blowpipe from all other bodies. 

Selenides ..—With the glass of silica and soda, the selenides 
behave as the sulphides; but the colour disappears sooner 
by a long blast than that produced by the sulphides. When 
a selenide is combined with a sulphide the selenium sublimes 
as selenium, while the sulphur is disengaged as sulphurous 
acid. If selenium be found with tellurium, the oxide of 
tellurium first sublimes, and finally, the selenium is deposited 
nearest the point heated. Sometimes sulphide of arsenic 
sublimes with the same appearances as selenium, but never 
with the same odour. 

Sulphates.— The presence of this class of bodies is ascer¬ 
tained in the same manner as sulphur, by means of the glass 
of soda and silica. The sulphates of the metals proper, 
when heated with charcoal in the close tube, ffive off 
sulphurous acid, which may be detected either by the smell 
or by its action on Brazil-wood paper. The metals of the 


BLOWPIPE REACTIONS. 


233 


alkalies and alkaline earths give no sulphurous acid when 
treated in this manner. 

Nitrates. —All the salts of nitric acid deflagrate with 
carbonaceous matters. This, however, is not characteristic, 
for the chlorates also possess this property. If any nitrate 
be heated in the close tube with bisulphate of potash, red 
fumes of nitrous acid are evolved. 

Bromides, heated with bisulphate of potash in the closed 
tube, give off vapours of bromine, which are similar in 
appearance to those of nitrous acid, but which recall the 
smell of chlorine. Under the head of Coloured Flames , 
another method of distinguishing bromine will be pointed 
out. 

Iodides, acted on by bisulphate of potash, give rise to 
splendid violet-coloured vapours, which are characteristic. 

•—(Also see Coloured Flames.) 

Chlorides, treated with bisulpliate of potash and peroxide 
of manganese, evolve chlorine, which may be recognised by 
its peculiar odour and yellowish-green colour.—(For further 
information, see Coloured Flames.) 

Fluorides, heated with bisulphate of potash, give rise to 
fluoric acid, which may be distinguished by its power of 
corroding glass. As fluorine occurs in very small quantities 
in certain minerals, and as it is rather difficult of detection, 
full instructions will be given. 

In case the mineral is very rich in fluoric acid, it may be 
mixed with microcosmic salt (previously fused), and heated 
at the extremity of an open tube, so that part of the current 
of air feeding the flame can pass into the tube. Aqueous 
fluoric acid is then formed, which can be recognised by its 
odour and by the corrosive action it exercises on the tube. 
If a slip of Brazil-wood paper be held at the opening of the 
tube, it becomes immediately yellow. On the contrary, 
when the acid exists but in minute quantity, as in fossils, or 
where it is combined with weak bases, or with a certain 
proportion of water, the substance can be heated in the 
close tube, after 'the introduction of a piece of moistened 
Brazil-wood paper. Hydro-fluosilicic acid is liberated by the 
heat, and a dull ring of silica deposited on the glass, a little 



234 


BLOWPIPE REACTIONS. 


above the assay; and lastly, the end of the Brazil-wood 
paper is turned yellow. Three or four per cent, of fluoric 
acid can be detected in this manner. 

Phosphates. —The following is the method recommended 
by Berzelius for the detection of phosphoric acid. ‘The 
substance to be assayed is dissolved in boracic acid, and, 
when a good fusion is effected, a piece of fine steel wire, a 
little longer than the diameter of the bead, is forced into it, 
and the wdiole then exposed to a good reducing flame. The 
iron is oxidised at the expense of the phosphoric acid, 
causing the formation of a borate of the oxide of iron and 
phosphuret of iron, which fuses at a sufficiently high 
temperature. The bead is then taken from the charcoal, 
enveloped in a piece of paper, and struck lightly with a 
hammer, by which means the phosphuret of iron is sepa¬ 
rated from the surrounding flux. It exists as a metallic- 
looking button, attractable by the magnet, frangible on the 
anvil, the fracture having the colour of iron. If the substance 
under assay contained no phosphoric acid, the iron wire will 
keep its form and metallic lustre, excepting at the ends, 
where it will be oxidated and burnt. The substance to be 
assayed ought not to contain sulphuric acid, arsenic acid, or 
any metallic oxides reducible by iron.’ 

Hydrates. —The presence of water in these substances 
can be ascertained by heating them in the close tube. If 
any water be present, it will vaporise and condense on the 
coolest portions of the tube. 

Silicates.— These compounds of silica with bases are 
decomposed by fusion with microcosmic salt, the silica being 
set at liberty, and the base combining with the phosphoric 
acid. When but a small quantity of microcosmic salt is 
employed, it often happens that the silica swells at the 
moment of decomposition, absorbing the liquefied mass. 
By adding a large quantity of the flux, the whole can be 
converted into a globule, which retains in suspension the 
semi-transparent tumefied silica. This can best be perceived 
when the glass is in a state of ignition. 

Coloured Flames. —There are a great number of substances 
best detected by the colours they impart to the flame of the 


COLOURED FLAMES. 


235 


blowpipe. Indeed, so important is this point, that it has 
been thought advisable to collect all the facts known on this 
subject into one place, rather than scatter them over the 
work. These experiments are best made in a dark room, 
and with a very small flame.* 


BLUE FLAMES. 


Large intense "blue . 
Pale clear blue 
Light blue . 

Blue 

Greenish blue 

Blue mixed with green 


Chloride of copper. 
Lead. 

Arsenic. 

Selenium. 

Antimony. 

Bromide of copper. 


GREEN FLAMES. 


Intense emerald green 
Very dark green, feeble 
Baric green . 

Bark green . 

Full green . . . 

Full green . 

Emerald green, mixed with blue 

Pale green . 

Very pale apple green 
Intense whitish green 
Bluish green 


. Thallium. 

. Ammonia. 

. Boracic acid. 

. Iron wire. 

. Tellurium. 

. Copper. 

Iodide of copper. 

I Bromide of copper. 
. Phosphoric acid. 

. Baryta. 

. Zinc. 

. Binoxide of tin. 


YELLOW FLAMES. 


Intense greenish yellow . . . Soda. 

Feeble brownish yellow . . . Water. 


RED FLAMES. 


Intense crimson 

Red . 

Reddish purple 
Violet 


Lithia. 

Strontia. 

Lime. 

Potash. 


Chlorine, combined with copper, gives an intense blue 
flame. This phenomenon may be produced as follows:— 
Take a piece of thin brass wire, and bend one end of it 
several times upon itself; place upon this some microcosmic 
salt, and fuse it until it has acquired a green colour. Then 
add to it the substance suspected to contain chlorine, and 
place it in the oxidising flame, just at the point of the blue 


* Griffin’s Blowpipe Analysis, page 148. 







236 


COLOURED FLAMES. 


flame ; if any chloride be present a splendid blue colour will 
be produced. 

Lead. — The blue colour produced by this metal is 
readily obtained. Fragments of a mineral must be held 
in the tongs, and powder may be assayed on charcoal. 

Arsenic, in the metallic state, gives rise to a light blue 
flame. 

Selenium and Antimony , when treated in the same manner, 
afford characteristic flames. 

Bromine. —If any substance containing bromine be placed 
in a bead of fused microcosmic salt on the brass wire, 
and then in the oxidising flame, a bright blue flame with 
emerald green edges will be produced. 

Boracic Acid. —The following is Dr. Turner’s process for 
the detection of boracic acid. ‘ The substance is to be mixed 
with a flux composed 1 part of fluor-spar and 4-.j parts 
of bisulphate of potash. This mixture is to be made to 
adhere to the moistened end of a platinum wire, and held at 
the point of the blue flame; at the instant of fusion, a dark 
green flame will be produced. It may also be produced by 
merely dipping the mineral in sulphuric acid, and exposing 
it to the blowpipe blast. In case a very small quantity of 
boracic acid is contained in a mineral, the following process 
may be employed :—The substance must be fused with 
carbonate of potash on charcoal, moistened with a drop or 
two of sulphuric acid, and then a few drops of alcohol: the 
latter will burn with a green flame when exposed to the 
flame of the blowpipe. 

Tellurium .—The peculiar flame given by this metal is 
produced by heating a portion of its oxide on charcoal in 
the reducing flame. 

Copper. —All the compounds of copper, except those in 
which bromine and chlorine enter, give a beautiful green 

J o o 

flame. The soluble salts give it per $e, but the insoluble 
require moistening with sulphuric acid. 

Iodine and Copper. —To the bead of microcosmic salt on 
the brass wire add any compound containing iodine, and a 
bright green flame will be produced when the mass is heated 
in the oxidising flame. 



COLOURED FLAMES. 


237 


Phosphoric Acicl. — The phosphates, when moistened 
with sulphuric acid, give a light green tint to the outer 
flame. 

Baryta .—The soluble salts of baryta give a light green 
colour to the outer flame when moistened with water. 

Zinc , when exposed to the blowpipe flame, burns with an 
intense whitish-green light. 

O C; 

Soda .—Any salt of soda, or substance containing soda, 
being exposed to the outer flame, gives a brush of intensely 
coloured flame, of a fine amber or greenish-yellow. 

Water .—Certain minerals containing water give a feeble 

O O 

yellowish tint to the flame. 

Strontia. —A.11 the salts of this substance which are soluble 
in water give a crimson tint to the flame, which does not 
endure after the substance is fused. Carbonate of strontia 
must be moistened with hydrochloric acid, and sulphate of 
strontia must be reduced to the state of sulphide by ignition 
with charcoal; it must then be moistened with hydrochloric 
acid ; after which treatment it will exhibit the characteristic 
flame. 

Lithia .—All that has been said of strontia applies to 
lithia, with the remarkable exception, that the coloured 
flame given by lithia is permanent, whilst that afforded by 
strontia is evanescent. 

Lime acts as strontia. 

Potash , treated as soda, gives a purplish light; but the 
reactions of potash and soda with oxide of cobalt are the 
best tests of their presence, combined with the peculiar light 
afforded by soda. 


238 


CIIAPTEB VIII. 

VOLUMETRIC ANALYSIS. 

Tiie main feature of volumetry is not so much analysis in 
the proper sense of the term, as the quantitative determina¬ 
tion of one principal constituent of a substance. 

This determination is done by means of solutions, con¬ 
taining a certain quantity of reagents in a certain volume, 
which is called a standard solution, the quantity used of 
such solution being measured by graduated tubes (burettes, 
pipettes, &c.). 

The reaction of a volumetric analysis can be of three 
different kinds, according to the reagent used and to the 
substance to be determined. 

1. The substance to be analysed being an acid or a base, 
it can be saturated by a suitable standard solution (saturation- 
analysis, used for acids, potash, soda, &c.). 

2. The substance to be assayed may be precipitated by 
the standard solution, and the completion of the process is 
observed when no further precipitate occurs (precipitation- 
analysis, e.g. Pelouze’s copper assay, Gay-Lussac’s silver- 
assay). 

3. The substance to be determined becomes, hy the stan¬ 
dard solution, either oxidised or reduced, and by the perform¬ 
ance of this process certain colours will appear or disappear, 
from which the completion of the process is to be observed 
(oxidation or reduction-analysis, e.g. Schwarz’s copper assay). 

These processes of volumetric analysis are frequently used 
in assaying. 

The principle of volumetric analysis may be fully explained 
by the following examples given by Fresenius.* 

4 Suppose we have prepared a solution of chloride of so- 

* Fresenius’s Quantitative Analysis, fourth edition, page 70. 


PRINCIPLES OF VOLUMETRIC ANALYSIS. 


239 


dium of such a strength that 100 c. c. will exactly precipitate 
1 grin, silver from its solution in nitric acid, we can use it to 
estimate unknown quantities of silver. Let us imagine, for 
instance, we have an alloy of silver and copper in unknown 
proportion, we dissolve 1 grm. in nitric acid, and add to the 
solution our solution of chloride of sodium, drop by drop, 
until the whole of the silver is thrown down, and ail addi¬ 
tional drop fails to produce a further precipitate. The 
amount of silver present may now be calculated from the 
amount of solution of chloride of sodium used. Thus, sup¬ 
posing we have used 80 c. c., the amount of silver present 
in the alloy is 80 per cent.; since, as 100 c. c. of the solu¬ 
tion of chloride of sodium will throw down 1 grm. of pure 
silver (i.e. of 100 per cent.), it follows that every c. c. of 
the chloride of sodium solution corresponds to 1 per cent, 
of silver. 

‘ Another example. It is well known that iodine and sul¬ 
phuretted hydrogen cannot exist together: whenever these 
two substances are brought in contact, decomposition imme¬ 
diately ensues, the hydrogen separating from the sulphur 
and combining with the iodine (I + HS=III + S). Iiydriodic 
acid exercises no action on starch-paste, whereas the least 
trace of free iodine colours it blue. Now, if we prepare a 
solution of iodine (in iodide of potassium) containing in 100 
c. c. 0’74T0 grm. iodine, we may with this decompose exactly 
OTgrrn. sulphuretted hydrogen; for 17 : 127 ::0T : 07470. 

‘ Let us suppose, then, we have before us a fluid containing 
an unknown amount of sulphuretted hydrogen, which it is 
our intention to determine. We add to it a little starch- 
paste, and then, drop by drop, our solution of iodine, until 
a persistent blue coloration of the fluid indicates the forma¬ 
tion of iodide of starch, and hence the complete decomposi¬ 
tion of the sulphuretted hydrogen. The amount of the 
latter originally present in the fluid may now be readily 
calculated from the amount of solution of iodine used. 
Say, for instance, we have used 50 c. c. of iodine solution, 
the fluid contained originally 0-05 sulphuretted hydrogen ; 
since, as we have seen, 100 c. c. of our iodine solution will 
decompose exactly 0T grm. of that body. 


240 


PRINCIPLES OF VOLUMETRIC ANALYSIS. 


4 Solutions of accurately known composition or strength, 
used for the purposes of volumetric analysis, are called 
standard solutions. They may be prepared in two ways, 
viz. (a) by dissolving a weighed quantity of a substance in a 
definite volume of fluid ; or ( b ) by first preparing a suitably 
concentrated solution of the reagent required, and then 
determining its exact strength by a series of experiments 
made with it upon weighed quantities of the body for the 
determination of which it is intended to be used. 

4 In the preparation of standard solutions by method a, a 
certain definite strength is adopted once for all, which is 
usually based upon the principle of an exact correspondence 
between the number of grammes of the reagent contained 
in a litre of the fluid, and the equivalent number of the re¬ 
agent (11=1). In the case of standard solutions prepared 
by method b , this may also be easily done, by diluting to the 
required degree the still somewhat too concentrated solution, 
after having accurately determined its strength ; however, 
as a rule, this latter process is only resorted to in technical 
analyses, where it is desirable to avoid all calculation. 
Fluids which contain the equivalent number of grammes of 
a substance in 1 litre, are called normal solutions ; those 
which contain of this quantity, decinormal solutions. 

4 The determination of a standard solution intended to be 
used for volumetric analysis is obviously a most important 
operation ; since any error in this will, of course, necessarily 
falsify eveiy analysis made with it. In scientific and accu¬ 
rate researches it is, therefore, always advisable, whenever 
practicable, to examine the standard solution—no matter 
whether prepared by method a or by method b, with sub¬ 
sequent dilution to the required degree—by experimenting 
with it upon accurately weighed quantities of the body 
for the determination of which it is to be used. 

4 In the previous remarks no difference has been made 
between fluids of known composition and those of known 
power; and this has hitherto been usual. But by accepting 
the two expressions as synonymous, we take for granted 
that a fluid exercises a chemical action exactly correspond¬ 
ing to the amount of dissolved substance it contains ; that, 



PRINCIPLES OF VOLUMETRIC ANALYSIS. 


241 


for instance, a solution of chloride of sodium containing 
1 eq. NaCl will precipitate exactly 1 eq. silver. This pre¬ 
sumption, however, is very often not absolutely correct. 
In such cases, of course, it is not merely advisable, but even 
absolutely necessary, to determine the strength of the fluid 
by experiment, although the amount of the reagent it con¬ 
tains may be exactly known ; for the power of the fluid can 
be inferred from its composition only approximately, and 
not with perfect exactness. If a standard solution keeps 
unaltered, this is a great advantage, as it dispenses with the 
necessity of determining its strength before every fresh 
analysis. 

4 That particular change in the fluid, operated upon by 
means of a standard solution, which marks the completion 
of the intended decomposition, is termed the final reaction. 
This consists either in a change of colour , as is the case 
when a solution of permanganate of potash acts upon an 
acidified solution of protoxide of iron, or a solution of 
iodine upon a solution of sulphuretted hydrogen mixed 
with starch paste; or in the cessation of the formation of a 
precipitate upon further addition of the standard solution, 
as is the case when a standard solution of chloride of sodium 
is used to precipitate silver from its solution in nitric acid; 
or in incipient precipitation , as is the case when a standard 
solution of silver is added to a solution of hydrocyanic acid 
mixed with an alkali; or in a change in the action of the 
examined fluid upon a particular reagent , as is the case 
when a solution of arsenite of soda is added, drop by drop, 
to a solution of chloride of lime, until the mixture no longer 
imparts a blue tint to paper moistened with iodide of potas¬ 
sium and starch-paste, &c. 

4 The more sensitive a final reaction is, and the more 
readily, positively, and rapidly it manifests itself, the better 
is it calculated to serve as the basis of a volumetric method. 
In cases where it is an object of great importance to ascer¬ 
tain with the greatest practicable precision the exact moment 
when the reaction is completed, the analyst may sometimes 
prepare, besides the actual standard solution, another, ten 

R 


242 


PRINCIPLES OF VOLUMETRIC ANALYSIS. 


times more dilute, and use the latter to finish the process 
carried nearly to completion with the former. 

4 But a good final reaction is not of itself sufficient to afford 
a safe basis for a good volumetric method ; this requires, as 
the first and most indispensable condition, that the particular 
decomposition which constitutes the leading point of the 
analytical process should—at least under certain known cir¬ 
cumstances—remain unalterably the same. Wherever this 
is not the case—where the action varies with the greater or 
less degree of concentration of the fluid, or according as 
there may be a little more or less free acid present; or 
according to the greater or less rapidity of action of the 
standard solution; or where a precipitate formed in the 
course of the process has not the same composition through¬ 
out the operation—the basis of the volumetric method is 
fallacious, and the method itself, therefore, of no value. 

4 When the new system of volumetric analysis first began 
to find favour with chemists, a great many volumetric 
methods were proposed, based simply upon some final reac¬ 
tion, without a careful study of the decomposition involved ; 
the result has been a superabundant crop of new volumetric 
methods, of which a great many are totally fallacious and 
useless.’ 

The only condition on which the volumetric system of 
analysis can be carried on successfully is, that the greatest 
care is exercised with respect to the graduation of the 
measuring instruments, and the strength and purity of the 
standard solutions. A very slight error in the analytical 
process becomes considerably magnified when calculated 
for pounds, hundredweights, or tons of the substance 
tested. The end of the operation in this method of analysis 
is in all cases made apparent to the eye. (Sutton.) 

Though our countrymen Faraday , Penny , Ure , Griffin , 
Scott, Sutton , and others, have rendered great services to' the 
development of volumetry, the German and French chemists, 
Liebig , Bunsen , Mohr , Gay-Lussac , Descroillez , have been 
the founders of it, and we are chiefly indebted to Mohr for 
the present high perfection of volumetry, which, saving a 
large amount of time and labour, as compared with the 




PROBLEM IN VOLUMETRIC ANALYSIS. 


243 


older methods of research, is, in many instances, to be pre¬ 
ferred to the latter methods. 

In the Annal. der Chemie und Pliarmacie , cxvi. p. 128, 
Dr. Mohr, of Coblentz, propounded a problem in volumetric 
analysis, and invited those interested in the subject to solve 
it. The first who did so was to receive one of Dr. Mohr’s 
burettes as a prize. Dr. Mohr asserted at the same time 
that he had himself already solved it. 

The problem was,— c To perform quantitative determina¬ 
tions without the use of weights, with volumetric solutions 
of unknown strength, and the strength of which must not be 
ascertained and regulated.’ Dr. Mohr received a number 
of communications, in which, however, some condition was 
violated; either a weight of some kind was used, or the 
strength of the test liquid was indirectly determined by 
saturated solutions of chloride of sodium (as in Liebig’s urea 
test), or in some other way. 

The problem was first solved by Dr. Pauli, of the Union 
Alkali Works, St. Helen’s, Lancashire, in December 
1860, in the following way. In one of the pans of a 
balance is put a piece of chemically-pure carbonate of soda, 
and in the other an equal weight of an undetermined soda, 
and both are measured by an acid of unknown strength. 
Suppose that in the first case 15 cubic centimetres, and in 
the second 11 cubic centimetres have been used, then 
15 : 11:: 100 : 73*33. The soda, therefore, contains 73*33 
per cent, carbonate of soda. 

The solution of the question, for which Dr. Pauli only 
cites a special case, is generally this :— 

Equal portions of the pure substance to be determined and 
the impure, are to be weighed off, one against the other, and 
are then to be measured with the same fluid ; then the cubic 
centimetres used for the pure substance represent 100 per 
cent., and the other number proportionately less. Suppose, 
for example, that it is proposed to determine the iron in an 
iron ore. A piece of pure iron wire is placed in the scale of 
a balance, and is exactly counterpoised by means of the pow¬ 
dered ore; both are then brought in solution as protoxide in 
the usual way, and are then treated with permanganate of 

R 2 


244 


PROBLEM IN VOLUMETRIC ANALYSIS. 


unknown strength. If oxide of iron is to be determined, 
pure oxide must be used instead of the wire. If potashes 
are to be examined, pure carbonate of potash (recently 
heated to redness) should be used. It would appear from 
this, that for every analysis the strength must be determined 
by the pure substance. This, however, is easily avoided if we 
put a sixpence into the scale-pan, and weigh with this both 
the pure and impure substance. The number of cubic cen¬ 
timetres of the fluid holds good as long as the same fluid 
and the same sixpence are used, and this number may be 
marked upon the bottle as expressing 100 per cent, for the 
same substance. 

This method is capable of universal application, and elimi¬ 
nates possible errors in weights and variations of tempera¬ 
ture. It is only necessary that the substance to be determined 
should be available in the pure state. But how is the pro¬ 
blem to be solved, if it remains as before, but with the 
further condition, c when the substance to be determined is 
not available in a pure state P ’ Dr. Mohr received two 
other solutions of the problem from Dr. Hiller and Herr 
Dietrich, both students in Heidelberg. Dr. Hiller has solved 
the question, even with the condition that the pure sub¬ 
stances should not be available, and in the same way as Dr. 
Mohr had already done it. For example,—if no chemically 
pure peroxide of iron can be obtained for a manganese 
determination, according to Dr. Hiller, pure permanganate, 
or pure bichromate of potash, can be employed to weigh off 
the manganese ; both are then converted by distillation with 
hydrochloric acid into chlorine, and then into iodine, and 
both fluids are then to be determined with the same 
unknown solution of hyposulphate of soda. Instead of using 
pure permanganate it would be better perhaps to use pure 
iodine to counterpoise the manganese, then to dissolve the 
iodine in iodide of potassium, and proceed as before. We 
have now to convert the value of the iodine into the value 
of an equal weight of pure peroxide of manganese, and 
express it in the cubic centimetres of hyposulphite used. 
As 43*57 Mn0 2 set 127 iodine at liberty, therefore any 
given weight of Mn0 2 would set at liberty or 2*914 


STANDARD SOLUTIONS. 245 

times as much iodine as is employed to counterbalance it. 
We have, therefore, to multiply the number of cubic centi¬ 
metres of hyposulphite which have been used for a quantity 
of iodine equal to the manganese by 2-915, and then to pro¬ 
ceed as if pure Mn0 2 and common manganese had been 
weighed together. 

If pure carbonate of soda cannot be obtained, pure car¬ 
bonate of lime may be used ; the cubic centimetres of the 
acid used must be multiplied by f§, that is, 1 atom of car¬ 
bonate of lime divided by an atom of carbonate of soda. 

STANDARD SOLUTIONS. 

We will only add here the preparation of permanganate 
of potash, and will give the preparation of other solutions 
when describing the processes for which they are used. 

The following description is condensed from Mr. Sutton’s 
excellent work on the subject.* 

The pure permanganate may be obtained very generally 
of the dealers in pure chemicals, but should it not be pro¬ 
curable when required, or the expense be too great, the so¬ 
lution may be prepared as follows :— 

Ten parts of caustic potash and 7 of chlorate of potash 
are fused in a Hessian crucible, then 8 parts of finely pow¬ 
dered peroxide of manganese added, and the whole well 
mixed with an iron rod; the crucible is kept at a dull red 
heat, and the contents stirred until, from the dissipation of 
the water, the mass loses its pasty state and becomes some¬ 
what friable ; continue the dull red heat, breaking the mass 
from the sides of the crucible and mixing altogether for a 
few minutes, then empty the contents into a clean copper or 
iron dish. When cool, it is to be coarsely powdered, put 
into a large flask or porcelain dish, and 20 or 30 times its 
weight of boiling water poured over it, then kept boiling 
gently until the solution assumes a deep purple rose colour. 
When the precipitated oxide of manganese has somewhat 
settled, the solution may be decanted into a large green 
glass bottle, and further diluted with the washings of the 


* 1 Volumetric Annhjsis y ' p. 84, et scq. 



246 


APPARATUS FOR VOLUMETRIC ANALYSIS. 


residue in the dish or flask to about the strength required 
for analysis. The solution so prepared contains a large 
quantity of alkali, and is constantly undergoing a slight 
change owing to its containing a portion of manganate of 
potash which slowly decomposes with precipitation of oxide 
of manganese. If the excess of caustic potash is saturated 
by an acid, the solution is far more stable. Mulder, there¬ 
fore, recommends that a stream of carbonic acid should be 
passed through the solution, frequently shaking it, until the 
potash is saturated ; an excess of acid does no harm; sul¬ 
phuric acid may also be used for the same purpose, but is 
not so recommendable. 

When the liquid thus treated has thoroughly settled, a 
portion may be decanted (not filtered through paper) into 
a convenient sized bottle for laboratory use. 

A very useful form of bottle for preserving it is the ordi¬ 
nary wash-bottle, or any common bottle fitted with the 
same arrangement of tubes. Burettes can then be filled 
with the solution without its frothing, and as the tube which 
enters the liquid does not reach the bottom of the bottle, 
the sediment, if any, is not disturbed ; another advantage is, 
that the solution does not come into contact with the cork, 
nor can any dust enter : the blowing tube may be closed by 
a very small cork. 

A solution prepared and kept as here directed will gene¬ 
rally preserve its strength unaltered for six months. 

The Instruments and Apparatus. 

The Burette —or graduated tube for delivering the stan¬ 
dard solution, may be obtained in a great many forms, under 
the names of their respective inventors, such as Mohr, Gay- 
Lussac, Binks, &c., but as some of these possess a decided 
superiority over others, it is not quite a matter of indiffe¬ 
rence which is used, and therefore a slight description of 
them may not be out of place here. The burette, with 
india-rubber tube and clip, contrived by Dr. Frederic Mohr 
of Coblentz, shown in Figs. 71 and 72, has the preference 
above all others for general purposes. 


APPARATUS FOR VOLUMETRIC ANALYSIS. 


247 


The advantages possessed by this instrument are, that its 
constant upright position enables the operator at once to 
read off the number of degrees of test solution used for any 
analysis. The quantity of fluid to be delivered can be regu¬ 
lated to the greatest nicety by the pressure of the thumb 
and finger on the spring clip, and the instrument not being 
held in the hand, there is no chance of increasing the bulk 


Fig. 71. 


Fig. 72. 




of the fluid by the heat of the body, and thus leading to in¬ 
correct measurement, as is the case with Biliks’ or Gay- 
Lussac’s form of instrument. The principal disadvantage, 
however, of these two latter forms of burette is, that a correct 
reading can only be obtained by placing them in an upright 


























THE BURETTE. 


2 48 

position, and allowing the fluid to find its perfect level. 
The preference should therefore, unhesitatingly, be given o 
Dr. Mohr’s burette, wherever it can be used; the greatest 
drawback to it is, that it cannot be used for permanganate 
of potash in consequence of its india-rubber tube, w 11 c i 
decomposes the solution. 

We are again indebted to Dr. Mohr for another form ot 

instrument to overcome this difficulty, viz., the foot burette, 

with india-rubber ball, shown in Fig. 73. 

The flow of liquid from 

the exit tube can be regu¬ 
lated to a great nicety by 
pressure upon the elastic 
ball, which is of the ordi¬ 
nary kind sold for children, 
and has two openings, one 
cemented to the tube with 
shellac, and the other at the 
side, over which the thumb 
is placed when pressed, and 
on the removal of which 
it refills itself with air. 

Gay-Lussac’s burette, sup¬ 
ported in a wooden foot, may 
be used instead of the above 
form, by inserting a good fit¬ 
ting cork into the open end, 
through which a small tube 
bent at right angles is passed. 
If the burette is held in the 
right hand, slightly inclined towards the beaker or flask into 
which the fluid is to be measured, and the mouth applied to 
the tube, any portion of the solution may be emptied out 
by the pressure of the breath, and the disadvantage of hold¬ 
ing the instrument in an horizontal position, to the great 
danger of spilling the contents, is avoided ; at the same time 
the beaker or flask can be held in the left hand and shaken 
so as to mix the fluids, and by this means the end of the 
operation more accurately determined. 














THE PIPETTE. 


249 


Fig. 74 will show the arrangement here described. 

The Pipette .—The pipettes used in volumetric analysis are 
of two kinds, viz., those which deliver one certain quantity 
only, and those which are graduated so as to deliver various 
quantities at the discretion of the analyst. In the former 
kind, or whole pipette, the graduation may be of three kinds, 
namely, 1st, in which the fluid is suffered to run out by its 
own momentum only. 2nd, in Fl( , 75 

which it is blown out by the 
breath. 3rd, in which it is 
allowed to run out to a definite 
mark. Of these methods the 
last is preferable in point of* 
accuracy, and should therefore be 
adopted if possible. The next II 50 CC 

best form is that in which the 
liquid flows out by its own mo¬ 
mentum, but in this case the last 
few drops empty themselves very 
slowly; but if the lower end of J 10CC 
the pipette be touched against 
the beaker or other vessel into 
which the fluid is poured, the 
flow is hastened considerably, 
and in graduating the pipette, it 
is preferable to do it on this 
plan. 

In both the whole and gradu¬ 
ated pipettes, the upper end is 
narrowed to about -J- inch, so that 
the pressure of the moistened 
finder is sufficient to arrest the 
flow at any point. 

Fig. 75 shows two whole pi¬ 
pettes, one of small and the other of large capacity, and also 
a graduated pipette of medium size. 

The Measuring Flasks .—These indispensable instruments 
are made of various capacities ; they serve to mix up stan¬ 
dard solutions to a given volume, and also for the subdivi- 































250 


COLORIMETRIC ANALYSIS. 


sion of the substance to be tested by means of the pipettes, 
and are in many ways most convenient. They should be 
tolerably wide at the mouth, and have a well-ground glass 
stopper, and the graduation line should fall just below the 
middle of the neck, so as to allow room for shaking up the 
fluid. 

Colorimetric Analysis is also used in assaying. It is 
based upon the fact that a coloured solution appears the 
more intense the more of the colouring substance it contains. 

If, therefore, a solution containing a certain amount of a 
substance and being in consequence of a certain intensity of 
colour, is prepared, it will be possible to obtain the solution 
under assay of an equal intensity of colour by appropriate 
dilution. 

By measuring the volume of the assay solution and taking 
into consideration the amount of the standard solution, the 
quantity of the substance contained in the assay solution 
may readily be calculated. 


TIIE ASSAY OF IRON 


251 


CHAPTER IX. 

THE ASSAY OF IRON. 

The ores of iron, properly so called, always contain the 
metal in the oxidised state, and in various degrees of 
purity. 

These ores are the following :— 

1. Magnetic Iron Ore (Fe 3 0 4 =Fe 2 0 3 -|-Fe0). When 
pure, it contains 72 per cent. Fe. 

2. Red Hjematite, anhydrous sesquioxide of iron (Fe 2 0 3 ). 
When pure it contains 70 per. cent. Fe. It occurs in dif¬ 
ferent varieties. 

3. Brown Hematite, brown iron ore , limoniie , hydrated 
sesquioxide of iron (2Fe 2 0 3 ,3H0). When pure it contains 
59*89% Fe, and 14*44 of water. It also occurs in many 
varieties, Bog iron ore being one of them. 

4. Spathic Carbonate, sparry iron ore , crystallised car¬ 
bonate of protoxide of iron (FeO,C0 2 ). When pure it con¬ 
tains 48*275 Fe. It generally contains some percentages, 
(2 to 15) of carbonate of protoxide of manganese, and 
carbonate of magnesia, frequently also some carbonate of 
zinc. 

5. Argillaceous Iron Ores, clay or clay-band ironstone , 
impure earthy carbonate of protoxide of iron . This mineral 
sometimes resembles compact limestone, sometimes greyish 
hardened clay. Its great specific gravity, its effervescing 
on the addition of an acid, and acquiring a brown-red 
colour on roasting, are sufficient means of identifying it. 

i The following is the result of an analysis of this class of 
ore by the Author; the specimen was from Ireland, county 
Leitrim:— 



252 


TIIE ASSAY OF IRON. 


Protoxide of iron.. 51’653 

Peroxide of iron ........ 3*742 

Oxide of manganese . . . . . . . *976 

Alumina 1*349 

Magnesia. *284 

Lime.*410 

Potash.. . . *274 

Soda *372 

Sulphur.. . • • *214 

Thosphoric acid ........ *284 

Carbonic acid ........ 31*142 

Silica ..6-640 

Carbonaceous matter and loss . . . . . 2*160 


100-000 


Blackband is a combustible schistose variety of this ore. 
The following analysis is also by the Author:— 


Protoxide of iron . 





. 20-924 

Peroxide of iron 





. *741 

Oxide of manganese 





. 1*742 

Alumina .... 





. 14-974 

Magnesia .... 

Lime ..... 





. *987 

. *881 

Potash 4 

Soda J 





. traces 

Phosphoric acid 

Silica. 





. *114 

. 26*179 

Sulphur .... 

Carbonic acid 





. *098 

. 14-000 

Carbonaceous matter 





. 16-940 

Water and loss 





. 2-420 






100 000 


6. Red Siliceous Iron (silica, water, peroxide and prot¬ 
oxide of iron). This mineral occurs only in rare cases in 
sufficiently large quantities to be used for iron smelting. 

Besides these iron ores the following substances, con¬ 
taining iron and used as fluxes, require assaying : Granite, 
Chlorite, Basalt, Pyrozene, Amphibole, and also some kind 
of slags (finery cinder, tap cinder, etc.). 

A. THE ASSAY OF IRON IN THE DRY WAY. 

It has been already mentioned that iron ores very seldom 
occur in a pure state, and the ores may be arranged for their 
assay in the dry way (and also for smelting) into five 
classes. 























THE ASSAY OF IRON IN THE DRY WAY. 


253 


1. Iron ores containing silica, lime, and another base, 
which ores are fusible, per se. 

2. Iron ores containing predominantly silica. 

3. „ „ „ „ lime. 

4. „ „ „ „ alumina. 

5. Iron ores containing a large amount of magnesia ; 
these ores are most difficultly rendered fluid. 

The flux used for assaying (and also melting) varies 
according to the nature of the predominant compound, and 
the quantity used according to the amount of that com¬ 
pound. 

If the composition of the ore is known, it is easy to ascer¬ 
tain the amount of flux necessary to form a slag with the 
bases or silica present; in most cases an extra quantity of 
the flux should be added, in order to produce a sufficient 
volume of slag to cover the button. 

According to Dr. Percy,* blast-furnace cinder of the fol¬ 
lowing formula may be taken as a type of the kind of slag 
desirable:— 

AlA, Si0 3 2 (3CaO, SiO s ). 

Its approximate composition per cent, is as under : 


Silica 
Alumina . 
Lime 


38 

15 

47 



- or about ■ 


1 

3 


parts 

v 

v 


The following mixtures of various fluxes, when fused, 
produce a slag which may be regarded as approximating to 
the above composition : 


Quartz . . 

. 1 

China clay 

• 2 { 

Lime . . 

. 2* 

Glass . . 

. n\ 

Lime . . 

. 2£ 

Shale or fire clay 3 1 

Lime . . 

• 2* 


Silica . . . 0 92 
Alumina . . 0 - 82 


Silica. 

Materials = to Aluminaf 


Silica . 
Alumina 


1-92 


'36 5 

per cent. 

0-82 

► ZZZ, - 

15-5 


2-5 


48-0 

v 

1-75' 

f 

35 

ft 

0-75 

■ = \ 

15 

tt 

2-5 

1 

50 

tt 

1*8' 


'35 

tt 

0-9 

b ZZZ - 

17 

tt 

2-5 


48 

tt 


According to Bodemann a compound of 56% silica, 30% 
lime, and 14% alumina forms a slag most easily rendered 


* Percy’s Metallurgy , p. 240. 

t 30% say of alkalies, lime, etc., on account of tlieir fusibility, are taken as 
equivalent to so much alumina. 
















254 


THE ASSAY OF IRON IN THE DRY WAY. 


fluid, but as it is found that this slag itself is not sufficiently 
fusible in a small assaying furnace (air furnace), an addi¬ 
tion of fluor-spar is given to the mixture, and in some cases 
(the iron ore being very difficultly rendered fluid), some 
borax is added, or a mixture of borax and fluor-spar. 

An exact knowledge of the mineralogical properties of 
the iron ores, and a due experience, will enable the assayer 
to properly adjust the fluxes without resorting to an analysis 
to find what amount of silica and bases are present. 

In some iron works of Germany the following propor¬ 
tions of fluxes are used :— 

F0 (T”^ch)° 0r !’ redllffimatite } 5to20 % chalk and 25o/ 0 fluorspar 

„ argillaceous brown iron ore 20 to 40 „ „ „ 30 to 40 „ „ 

» bog iron .... 50 „ „ „ 50 „ „ 

„ spathose iron ore . . . 10 to 15 „ china clay „ 20 to 25 „ „ 

„ finery cinder . . . 20 to 25 „ chalk „ 20 to 25 „ „ 

Air-furnaces are best adapted for assaying iron ores where 
many assays are required. And naked crucibles, either of 
clay or blacklead, or crucibles lined with charcoal, are em¬ 
ployed ; the latter are preferable. 

The button of metal does not adhere to naked pots, but 
the slag adheres very strongly; so much so, that it cannot 
be detached with any degree of accuracy for weighing 
(which in some of M. Berthier’s processes is of importance). 
Black-lead pots allow neither the slag nor button to adhere, 
but the former dissolves much argillaceous matter from the 
pot, so that its weight is greatly increased, and the assay 
cannot be verified. In naked crucibles, charcoal must 
always be added to the assay, to reduce the oxide of iron; 
in which case, if an excess be added, it prevents the button 
from completely forming, so that globules remain in the 
slag (with care this may, however, be avoided). Neither 
do naked crucibles resist the fire as well as those lined 
with charcoal, because the lining supports the sides when 
they soften. The charcoal lining also allows the assay to 
be finished without adding any re-agent to the ore ; the 
button can be readily taken out, because it does not 
adhere to the charcoal; and lastly, the earthy matters in 
the ore, which have formed a slag, may be collected and 


FLUXES FOR THE ASSAY OF IROX. 25 5 

weighed; or, if we have added any flux to the ore, the 
total weight can also be ascertained. 

After having finely powdered and sifted the iron ore, a 
determinate weight must be taken (200 grains is the most 
convenient quantity in ordinary cases); a certain weight 
of the requisite flux must be well mixed with the ore in 
a mortar, and the whole placed in the crucible (which must 
be lined with charcoal), in which it is gently pressed by a 
pestle or other appropriate instrument, and covered with 
a slight layer of fluor-spar. The crucible is then filled with 
successive layers of charcoal powder, slightly moistened with 
water ; a cover luted on it, and the whole placed in the 
lire. The fire is allowed to burn gently for about an hour, 
and the heat raised to whiteness for about the same time, 
or a little longer ; the crucibles are taken out, allowed to 
cool, and the button and flux removed. 

The whole fused mass is then weighed, and then the 
button of metal carefully separated from the flux, and 
weighed; sometimes small globules of iron are found adhering 
to the flux, in which case they must be removed, and added 
to the button before weighing. Even when very small, 
their removal can be readily effected ; the flux is finely pul¬ 
verised, and placed on a sheet of paper; a magnet is then 
drawn gently over its surface, which method of procedure 
will ensure the separation of all metallic particles. The 
formation of such globules is prevented, to a great extent, 
by the thin layer of fluor-spar. If the weight of metal 
obtained be now deducted from the weight obtained in the 
first weighing, the difference will be the weight of flux. 

It sometimes happens that the assay is not fused, or but 
imperfectly so. This can happen from two causes ; firstly, 
because the heat has not been sufficiently strong or long con¬ 
tinued ; secondly, the flux has not been employed in proper 
proportions, or has not been calculated to form fusible com¬ 
pounds with the foreign matters mixed with the oxide of 
iron. In the imperfectly fused buttons the iron is dissemi¬ 
nated in globules through the whole mass of slag, or forms a 
scoriform button mixed with much slag, without the possi¬ 
bility of complete separation. 


*256 


TIIE ASSAY OP IRON. 


The slag ought to be well fused, colourless, transparent, 
or white, light-grey. 

Good buttons of metal, when wrapped in pieces of thin 
tin plate, and struck with a heavy hammer on the anvil, 
flatten slightly before they break; they ought to be grey or 
greyish-white, and the grain fine, or tolerably fine. Bad 
buttons break readily without changing form, some even 
pulverise; they are generally very white and crystalline on 
the surface. 

Several assays (at least two) ought to be made of the 
same ore, and the buttons of iron obtained should not vary, 
or only very little—not more than -|th of a per cent. The 
buttons always contain foreign substances (2 — 6 per cent.), 
chiefly carbon, and silicon, frequently also phosphorus, 
sulphur, arsenic, manganese, titanium, and chromium. 

Berthier recommends the following method for estimating 
the other, chiefly slag-forming, components of iron-ores. 
The operations of this method are comprised in roasting, or 
calcining, to drive off any volatile or combustible matters, 
and in treating the ore with certain acids, the object of which 
is to ascertain the amount of insoluble matter, by difference 
of weight, before and after the action has taken place. 

The hydrated ores are calcined to estimate water; and 
those containing manganese, to reduce it to a fixed and 
known state of oxidation (sesquioxide). The carbonates 
are roasted to expel carbonic acid, and the ores from the 
coal formations to burn the combustible matter with which 
they are mixed. 

Slags and dross are also roasted to free them from char¬ 
coal. A simple calcination sometimes is sufficient, as in the 
case of carbonates; but where mixtures of per- and prot¬ 
oxide of iron are to be assayed, they must be subjected to a 
long roasting, in order to convert all the contained prot¬ 
oxide into peroxide. 

Diluted and cold nitric or acetic acids are employed for 
minerals whose matrix is purely calcareous or magnesian, as 
these acids dissolve the earthy carbonates, without attacking 
either stones, clay, or the oxides of iron. The residue is 
to be well washed, dried, and weighed, and the amount of 


THE ASSAY OF IKON. 


257 


carbonates calculated by tlie difference. It is now to be 
treated with boiling hydrochloric acid, or, what is prefer¬ 
able, aqua regia . The ores which contain substances in¬ 
soluble in these acids are generally of a clayey or flinty 
nature. These are to be weighed, and according to their 
weight that of the flux to be added in the assay is deter¬ 
mined, as will be shown hereafter. 

It must be borne in mind, however, that the clays are 
not absolutely insoluble in hydrochloric acid, for a certain 
quantity of alumina is always dissolved, which is generally 
greater in proportion to the amount present in the iron ore. 

The ores containing titanium are boiled with concentrated 
sulphuric acid, after they have been reduced to the finest 
possible state of division. All the oxides of iron, titanium, 
and manganese, are dissolved, and the stony gangues which 
resist the action of this acid can be estimated. The utility 
of this estimation will be pointed out as we proceed. 

When all the operations necessary for each particular 
case have been completed, we know the proportion of vola¬ 
tile substances, of substances soluble in acetic acid, and 
those insoluble in hydrochloric and sulphuric acids, contained 
in the substance under assay. 

Let A be the weight of the rough or non-calcined ore: B 
the weight of the same calcined ; 0 the weight of the fluxes 
in a rough state; D the weight of the same calcined ; P the 
weight of matter insoluble in hydrochloric or sulphuric 
acids ; E the weight of the fixed substances soluble in acetic 
or nitric acids,—a weight which can be readily calculated 
when we know the loss which the ore, not treated by acids, 
suffers by calcination, and the residue of the treatment of 
this substance by acetic or nitric acid; M the weight of the 
button of metal and scattered globules; S the weight of the 
slag; and 0 the loss of weight in the assay which represents 
the quantity of oxygen disengaged during the reduction. 

The following is the disposition of the data from which, 
at one view, all the useful results of the assay can be deter¬ 
mined. 

In the assay has been employed :— 


s 


258 


TIIE ASSAY OF IRON. 


. A, rough oro = calcined ore 
B, of rough fluxes added = fixed flux . 



Total of fixed matter B + D 


The result has been :— 


Metal — M 
Slag — S 


J Total 


. M + S 


Loss 


O 


Fluxes . . . . . 

Vitrifiable matters. 

Substances insoluble in hydrochloric acid, &c. 
Substances soluble in hydrochloric acid, &c. . 
Substances soluble in acetic acid .... 
Substances insoluble in acetic acid, and soluble in 


D 

S - D 
T 

S—D—T 
R 


hydrochloric acid 


. s—D—T—R 


When the iron in the substance assayed is in a known 
degree of oxidation, and when but little manganese is 
present, the quantity of oxygen O ought to correspond very 
nearly with the quantity of metal M produced; if it does, 
the assay must be correct. 

A rigorous correspondence between the two numbers, 
however, cannot always be obtained, because the iron is not 
pure, but always contains carbon, so that in ordinary assays 
the peroxide of iron loses but from twenty-eight to twenty- 
nine per cent, of oxygen. 

On the other hand, the quantity of iron remaining in the 
slag makes up in part for the carbon combined with the 
metal reduced ; but when the assay has been made with 
a suitable flux, the quantity of oxide remaining is very 
small, and never exceeds one per cent, of the weight of 
the slag. When the iron is in an unknown degree of 
oxidation, the loss 0 produced in the assay gives the degree, 
if it has been made without accident; but if there is any 
doubt, and the result is of importance, the assay must be 
recommenced for verification. If the ferruginous matter 
contain manganese, and if that metal be in the state of 
protoxide, the verification just described can be made with¬ 
out modification, because the manganese dissolved in the 
slag is always at the minimum of oxidation : and when a 
sufficient quantity of flux is employed, the amount reduced 






THE ASSAY OF IRON. 


250 


is of no consequence. But when the manganese is in the 
state of red oxide, it parts with a certain quantity of oxy¬ 
gen on being reduced to the minimum of oxidation, and 
which quantity is estimated in the loss 0, so that a perfectly 
accurate verification cannot be made. Nevertheless, the 
difference between the loss 0, and the quantity of oxygen 
calculated from the metal M, cannot be very great, because 
the red oxide of manganese loses but *068 of oxygen in its 
transformation to protoxide. 

If the assay has been made with care, the loss of oxygen 
indicates the amount of iron in a very approximate manner, 
and nearly always with an exactitude which is surprising to 
those not accustomed to this kind of operation. 

Titanic acid behaves in iron assays exactly as the oxides 
of manganese ; it disengages at most but *06 of oxygen 
when dissolved in the earthy glasses in contact with char¬ 
coal. 

The following process of Professor Abel for the complete 
assay of iron and iron ores is of great interest, and therefore, 
may find here a proper place. It is. extracted from the 
4 Report of Experiments on British Irons, Ores, and for the 
Manufacture of Cast-iron Ordnance.’ 

4 In conducting a large series of analytical examinations 
of a quantitative character, which have been undertaken, 
not simply to furnish results of scientific interest, but with 
a view to be of use in considerations of a practical charac¬ 
ter, it is not only admissible, but necessary, that some dis¬ 
crimination should be exercised in determining the extent 
of detail of such examinations, so that, on the one hand, 
a proper knowledge be obtained of the proportions of all 
the important and characteristic components of a substance, 
while, on the other hand, no great unnecessary expenditure 
of time and labour be incurred in researches on the exist¬ 
ence or proportions of constituents which occur in minute 
quantities in the substances examined, and have not yet 
been discovered to exert any influence on its chemical or 
physical character. 

4 Thus, the existence in cast iron of metals, such as tita¬ 
nium, calcium, magnesium, nickel, copper, lead, &c., has 


200 


TIIE ASSAY OF IRON. 


been traced by minute analyses of various samples by 
different chemical authorities, and the proportions in which 
they occur have also frequently been determined; but 
it is only when some foreign metal, such as copper, lead, or 
arsenic, has been found to exist in a sample of cast iron, 
in a larger proportion than usual, that it has been proved 
to exert some marked and well-established influence over 
the character of the metal. 

‘It may, therefore, be safely inferred, in the present state 
of our knowledge, that modifications in the properties of 
cast iron are not dependent upon the presence or absence 
of minute proportions of such foreign metals, and that re¬ 
searches having in view the discovery or the determination 
of the proportions of these constituents, do not at present 
possess any practical interest, and are only advisable : 

4 1. In conducting analyses of specimens of peculiar in¬ 
terest for purposes of scientific record. 

6 2. In undertaking special researches with a view to 
ascertain whether, and to what extent, these constituents 
influence the properties of cast iron. 

4 Such researches as those last referred to are unquestion¬ 
ably of great interest, and, if pursued to a sufficient extent, 
may possibly lead hereafter to important practical results. 
Their objects differ, however, from those of the investigation 
the results of which are embodied in this Eeport, and 
which was undertaken with a view to ascertain, by an 
application of our present knowledge of the chemical and 
physical properties of cast iron, the relative qualities of 
various descriptions of pig iron submitted by numerous 
manufacturers. 

4 There is no question, however, that it is in most instances 
very important to perform complete analyses of materials 
which are to be employed for the extraction of metals: for 
as these, at the high temperature necessary in the process 
of their reduction from ores, are endowed with powerful 
affinities for many of the frequent constituents of such ores, 
their properties will suffer more or less important modifica¬ 
tion by union with some of these components in the course 
of their reduction. 


TIIE ASSAY OF IRON. 


2G1 


c The quality of the product may therefore be, to some 
extent (when the treatment is under control), predicted 
from the results of a complete examination of the materials 
employed. It is, consequently, not only essential to ascer¬ 
tain the general composition of an ore, for the purpose of 
determining the nature and proportions of the auxiliary 
materials (fluxes) to be associated with it in the reduction 
process, but it is also of considerable importance to ascertain 
whether, and in what proportions, such constituents (as 
foreign metals, sulphur, and phosphorus) are contained in 
the ores, as are likely to enter into the composition of the 
product and exert an influence upon its properties. 

4 In the chemical examination of the lame series of iron 

O 

samples and materials employed in their manufacture the 
system of analysis adopted has been based upon the princi¬ 
ples embodied in the foregoing remarks. 

4 The samples of ores received from the manufacturers have 
been all submitted to complete analysis, excepting in the 
following instances:— 

6 1. In one or two cases where the samples were found to 
be identical in character with some of the series of ores 
recently submitted to complete analysis at the Government 
School of Mines, under Dr. Percy, the results of which 
have been published in the 44 Memoirs of the Geological 
Survey of Great Britain.” 

4 The close resemblance of the samples to those above 
alluded to was established by a comparison with the de¬ 
scriptions given of the ores in the Government Eeport, by a 
careful examination of them made by Mr. Spiller, who 
performed a large number of the analyses alluded to in 
that Eeport while at the School of Mines, and was well 
acquainted with all the specimens examined ; and lastly, 
by a determination of the most important constituents of 
the samples received (e.g. the oxide of iron and phosphoric 
acid), and a comparison* of the results with those of the 
published analyses. 

4 In these instances, as a complete analysis of the samples 
would have involved a very considerable unnecessary ex¬ 
penditure of time, it was not undertaken; but the detailed 


‘2G'2 


THE ASSAY OP IRON. 


analyses of the ores, to which the samples corresponded, 
have been extracted from the Government Eeport. 

4 2. A few of the ores received had been submitted to 
the roasting process. As the effect of this treatment of an 
ore is greatly to modify its original composition, partially 
expelling certain constituents, and altering the arrangement 
and state of combination of others, a detailed analysis would 
afford no correct indication of the original nature of the ore. 
In such instances, therefore, it was only considered im¬ 
portant to determine the per-centages of iron and of those 
constituents which might affect the quality of the metal 
obtained from the ore—the phosphoric acid and sulphur. 

4 3. The ores sent by some manufacturers were identical 
in their nature with those from other works, and of which 
complete analyses have been made. In these instances the 
most important constituents of the samples in question have 
alone been determined, references having been made, when 
needful, to the full analyses. 

4 The minerals employed as fluxes were all submitted 
to complete analysis, except in one or two instances, when 
their identity with samples already analysed was established 
by the determination of one or two constituents. 

4 The examination of the fuel was partial, the only im¬ 
portant object being to determine to what extent it might 
contain mineral matters possibly prejudicial to the quality 
of the metal reduced by its means. The examinations 
therefore included determinations of the amount of sulphur 
in the coal or coke, and the amount and character of the 
ash furnished by incineration. It was also considered in¬ 
teresting to determine the amount of coke furnished by the 
different samples of coal. 

4 The analyses of the samples of iron were, for the reasons 
already stated, limited in most instances to the determination 
of the proportions of those constituents which have already 
been satisfactorily proved to exert some influence on the 
quality of the pig iron, or on the results obtained by sub¬ 
mitting it to subsequent processes of manufacture. 

4 The constituents in question are manganese, silicon, 
phosphorus, sulphur, and carbon. 


THE ASSAY OF IRON. 


2GS 


4 With reference to the last named substance, it may be 
necessary to observe, that almost all the specimens of pig 
iron examined which are included in this report were varie¬ 
ties of grey iron, and that but very few of the samples con¬ 
tained any appreciable amount of carbon in the combined 
form. 

4 It was, therefore, of no importance or interest to deter¬ 
mine the minute portions of carbon existing in the samples 
in the latter form, and this was proved by special examina¬ 
tions of a few of the light grey samples of the series, in 
which the amount of combined carbon was not found to 
exceed at highest 0'35 per cent. : and also by the determina¬ 
tion of the total amount of carbon in a sample of No. 1 pig 
iron, the result obtained being identical with that afforded 
by the direct estimation of the carbon existing as graphite. 

4 In two or three instances it was considered interesting 
to examine specially for certain foreign metals which had 
been found to exist in appreciable quantities in some of the 
ores from which the samples thus examined had been ob¬ 
tained. 


I. Analyses of the Iron Samples. 

4 Preparation of the SamjAe .—Preparatory to its examina¬ 
tion, the metal was reduced to a suitable state of division 
by boring, turning, or planing. In the case of white iron 
it was broken to a coarse powder in a steel-crushing mortar. 
It was considered preferable to prepare an average sample 
of the pig by boring across it, so that a fair proportion of 
the graphite, which was occasionally concentrated towards 
the centre of the pig, might be included in the sample. 
The fine borings obtained in this way were further reduced 
when necessary, and thoroughly mixed by trituration in a 
Wedgwood mortar. 

4 Chemical Analysis .—In the analysis of pig iron the 
proportion of the following constituents were usually deter¬ 
mined : manganese, carbon, silicon, sulphur, phosphorus, 
and, in certain cases, metals such as arsenic, lead, and 
copper, when their existence in appreciable quantity had 


2G4 


THE ASSAY OP IRON. 


been discovered in the ores from which the iron had been 
obtained. 

‘For this purpose four portions were usually weighed 
out:— 

a. 100 grains, for sulphur, carbon existing as graphite, 
silicon, and manganese. 

b. 50 grains, for phosphorus. 

c. 50 to 100 grains, for determining the existence and 
amount of combined carbon. 

d. 500 grains, for metals existing in the iron in minute 
proportions. 

4 Sulphur.— 100 grains of the iron borings were slowly 
dissolved in concentrated hydrochloric acid, the evolved gas 
being passed through a solution of acetate of lead, slightly 
acidified with acetic acid, the sulphuretted hydrogen, dis¬ 
engaged together with hydrogen, precipitated the sulphide 
of lead, which was collected on a filter, washed, burnt, and 
subsequently (in the customary manner) converted into 
sulphate of lead, from the weight of which the per-centage 
of sulphur was calculated. 

4 The contents of the flask, after the metal had been fully 
acted upon, were transferred to a porcelain basin and eva¬ 
porated to dryness, the mass digested with concentrated 
hydrochloric acid, and water afterwards added. The in¬ 
soluble residue consisting of silicic acid and graphite, was 
collected on a filter, the filtrate being reserved for the 
estimation of manganese. 

4 Carbon, as Graphite.— The mixed silicic acid and erra- 

o 

phite were separated by the action of a warm solution of 
pure potassa, when the silicic acid was dissolved, the graphite 
which remained insoluble was again collected, washed with 
dilute hydrochloric acid and water, and dried. It was 
afterwards carefully removed from the paper by scraping 
with a knife blade, and transferred to a platinum crucible, 
in which, after exposure for some time to about 300° F., it 
was weighed. Upon subsequently burning the graphite in 
a muffle, it usually left a very small quantity of reddish ash, 
which was deducted from the former weight. 

4 Silicon.—T he amount of silicic acid, dissolved by the 



THE ASSAY OF IRON. 


2G5 


potassa, was recovered in the usual manner, by evaporation 
with hydrochloric acid ; the residue was digested with water 
collected, washed, dried, and weighed. The amount of 
the silicon in the iron was calculated from the silicic acid 
obtained. 

4 Manganese.— The hydrochloric acid solution, separated 
from the silicic acid and graphite, was divided into two 
equal portions, one of which, representing 50 grains of iron, 
was always sufficient for the estimation of the manganese. 
The iron in the liquid having been per-oxidised by boiling 
the hydrochloric acid solution, and adding occasionally a 
little chlorate of potassa, the acid was to a great extent 
neutralised by addition of carbonate of ammonia. Suffi¬ 
cient acetate of ammonia was afterwards added for the 
conversion of the chloride of iron into acetate, and the 
liquid was boiled, when the iron was completely separated 
as insoluble basic acetate. The filtrate containing the 
manganese was rendered alkaline with ammonia, and, 
after the addition of a few drops of bromine, set aside 
for about eighteen hours. The hydrated binoxide of 
manganese which had separated from the liquid, was 
afterwards collected, washed, dried, and ignited at a high 
temperature, when it was weighed as manganoso-manganic 
oxide (Mn 3 0 4 ), which furnished, by calculation, the quantity 
of manganese. 

4 Phosphorus. —For the estimation of phosphorus, 50 
grains of the iron borings were acted upon with warm nitro- 
hydrochloric acid, in a flask with a long neck, and, after 
complete solution of the metal, the contents of the flask 
were transferred to a porcelain basin and evaporated to 
dryness; the residue was moistened with concentrated hy¬ 
drochloric acid, and again evaporated, so as thoroughly 
to expel nitric acid. The residue then obtained was dis¬ 
solved in hydrochloric acid, the solution diluted, filtered, 
nearly neutralised with carbonate of ammonia, and the iron 
in solution reduced to protoxide by the addition of sulphite 
of ammonia to the gently heated liquid, and the subsequent 
careful addition of dilute sulphuric acid to expel excess of 
sulphurous acid. Acetate of ammonia and a few drops of 



2G6 


TIIE ASSAY OF IRON. 


solution of sesquichloride of iron were then added, and 
the liquid boiled, when the phosphoric acid was pre¬ 
cipitated as basic phosphate of sesquioxide of iron, with 
some basic acetate. The liquid was rapidly filtered, with 
as little exposure to the air as possible, the precipitate 
was slightly washed and dissolved in hydrochloric acid, 
the solution neutralised with carbonate of ammonia, and a 
mixture of ammonia and sulphide of ammonia added; 
it was then gently heated, to ensure the conversion of the 
phosphate into sulphide of iron. The latter was after¬ 
wards removed by filtration, washed with dilute sulphide 
of ammonium, and the phosphoric acid was precipitated 
from the solution in the usual manner as ammonio-phos- 
phate of magnesia, and weighed as pyro-phosphate of 
magnesia, from the amount of which the phosphorus was 
calculated. 

4 Combined Carbon.— After numerous comparative trials 
of the several methods in common use for determining 
the total amount of carbon in cast iron, that which was 
ultimately adopted (after necessary experiments had fully 
established its accuracy) consisted in dissolving the metal in 
an acid solution of chloride of copper, collecting and wash¬ 
ing the insoluble residue which remained after the complete 
action of this solvent, and submitting it, -when dry, to 
combustion with oxide of copper in a current of oxygen, 
the source of heat employed being the gas combustion 
furnace. The total amount of carbon in the iron was then 
calculated from the weight of carbonic acid absorbed by 
solution of potassa in the usual manner. The carbon, 
existing in a state of combination with the iron, was repre¬ 
sented by the excess which this process afforded over that 
of the direct estimation of the carbon as graphite, in the 
manner already described. 

4 Minute Proportions of Foreign Metals. —About 400 or 
500 grains of the iron were employed in the examination 
for metals precipitated by sulphuretted hydrogen, e.g ., lead, 
copper, arsenic, Ac. The iron was dissolved in hydrochloric 
acid, and the solution, diluted and partly neutralised with 
carbonate of soda, was submitted to the action of sulphur- 


THE ASSAY OF IRON. 


267 


etted hydrogen. After saturation with the gas, the liquid 
was allowed to stand at rest for several hours, and the small 
quantity of sediment which had subsided was examined for 
metals by the ordinary analytical processes. 

II .—Analysis of the Iron Ores. 

‘ The analytical processes employed for the separation of 
the various constituents occurring in iron ores were, in great 
measure, identical with those employed in the examination 
of metallic iron. Thus, the estimation of oxide of man¬ 
ganese was conducted in a precisely similar manner; and, 
with the exception that no process of reduction was re¬ 
quired in the case of clay ironstones and other ores con¬ 
taining the iron already in a state of protoxide, the phosphoric 
acid was determined by the same process as that employed 
for the estimation of phosphorus in pig iron. The amount 
of metallic iron, and its condition of oxidation in the ore, 
were determined by Marguerite’s volumetrical method, 
with standard solution of permanganate of potassa ; while 
the proportions of lime and magnesia, carbonic acid, water, 
hygroscopic and combined, insoluble residue, and the 
nature of this latter, were determined by following the ana¬ 
lytical processes invariably employed in mineral analyses 
of this description. 

c Sulphur was estimated by fusion of the ore (or, in the 
case of clay ironstone of the clay only) with a mixture of 
pure carbonate of soda and nitre; the sulphuric acid being 
precipitated by chloride of barium, from the acidified 
solution of the fused mass, and the sulphate of baryta 
collected, burnt, and weighed as usual. The hydrochloric 
acid solution of the ironstone was examined for sulphuric 
acid, but it was seldom that more than a trace of sulphur 
was detected in that form. 

III. Analysis of the Samples of Fluxes. 

6 These materials, consisting of limestone, burnt shale, &c. 
were analysed by a method precisely similar to that em- 


•208 


TIIE ASSAY OF IRON. 


ployed in the examination of the ores. In the tabulated 
statement showing the composition of the limestones, the 
amount of carbonate of lime is, in some few instances, 
represented by the difference, after the whole of the other 
constituents had been determined. In such cases the sum- 
total of constituents is necessarily expressed by 100 exactly.’ 


B. THE ASSAY OF IRON IN TIIE WET WAY. 

Fuchs' Method .—A suitable quantity (10 grs.) of the 
finely pulverised iron-ore (pig-iron, &c.), is dissolved in an 
excess of concentrated hydrochloric acid, and the resulting 
protocliloride of iron is changed into sesquichloride of iron, 
by the addition of chlorate of potash; the chlorine is 
then to be expelled by heating the liquid. The latter is 
diluted with water, and perfectly clean strips of clectrotyped 
copper (15—20 grs.) previously exactly weighed, are put 
into it. These operations must be done in a glass flask, 
tightly closed by a cork, through which a narrow glass 
tube passes. The liquid is now heated to the boiling-point, 
and kept at this temperature till the original dark-brown 
or yellow colour of the liquid changes to a light-yellow 
green or light blue-green colour. Then all the sesquichlo¬ 
ride of iron will be reduced to protochloride in consequence 
of the formation of subchloride of copper. The open part 
of the glass-tube is now hermetically closed, and the liquid 
allowed to cool. The flask is then filled with hot water, 
and the liquid decanted from the undissolved copper. The 
latter is washed, first with diluted hydrochloric acid, and 
afterwards repeatedly with water; it is then dried and 
weighed. The amount of iron contained in the assayed sub¬ 
stance may be calculated by the loss of copper, that amount 
of iron standing in the same proportion to the dissolved 
quantity of copper as the equivalent of iron (28) to the 
equivalent of copper (3T7). 28 parts of iron correspond 

to 36 parts of protoxide of iron and to 40 parts peroxide 
of iron. 

Some iron-ores are very difficultly or only incompletely 


THE ASSAY OF IRON. 


2C9 


dissolved in hydrochloric acid ; they must then be previously 
fused with carbonate of soda and potash. 

The above method is based upon the fact that chemically 
pure hydrochloric acid is not able to dissolve copper 
without the presence of atmospheric air, and that this 
acid dissolves copper if peroxide of iron is present. The 
quantity of copper dissolved is then proportional to the 
amount of peroxide of iron present. In this process 
protochloride of iron and subchloride of copper are formed, 
Fe 2 Cl 3 + 2 Cu = 2FeCl + Cu 2 Cl. Two equivalents of cop¬ 
per (63,4 parts) therefore reduce 1 equivalent of peroxide 
of iron (80 parts) ; the latter containing 2 equivalents of 
iron (56 parts). 

In case the iron ore contains arsenic, the latter must be 
previously removed by fusing the iron ore with 3 parts dried 
carbonate of soda, and by lixiviating the fused mass. 

If the iron ore contains titanium it will be necessary to 
decompose the chloride of iron by copper at a lower tempe¬ 
rature than the boiling-point. 

If the iron ore contains peroxide of iron together with prot¬ 
oxide of iron, the same process may be used to determine 
the quantities of both combinations. The process is then to 
be performed twice, once before oxidation and the second 
time after it. The first operation will show the quantity of 
peroxide of iron which the iron-ore originally contained, as 
the copper only acts upon peroxide of iron, and not upon 
protoxide of iron. 

Marguerite's Process .—This method of analysis is 
based on the reciprocal action of salts of the protoxide of 
iron and mineral chameleon (permanganate of potash—KO, 
Mn 2 0 7 ), whereby a quantity of the mineral chameleon is 
decomposed exactly proportionate to the quantity of iron. 

Thus, in any given solution of iron at its maximum of 
oxidation, such as it more commonly exists in the mineral 
it is only necessary to bring it to the minimum of oxidation, 
and then to add gradually a solution of permanganate of 
potash of a known strength. As long as a trace of protox¬ 
ide remains to be peroxidised the colour of the chameleon 
is destroyed ; but it is at length noticed that the colour of 



270 


THE ASSAY OF IRON. 


the last drop added is no longer destroyed, but communi¬ 
cates a pink tint to the whole of the solution. This reaction 
indicates that the operation is terminated, and the quantity 
of iron in solution corresponds to the amount of permanga¬ 
nate added. 

This reaction may be expressed by the following equa¬ 
tion :— 

K0,Mn 2 0 7 + lOFeCl + 8HCl=2MnCl + KC1 + 5Fe 2 Cl 3 8IIO. 

It will be seen that 1 equivalent of permanganate of 
potash is capable of peroxidising 10 equivalents of protoxide 
of iron. It is hardly necessary to mention that the solution 
of the iron should contain a sufficient excess of acid to hold 
in solution the peroxide of iron formed, and also the protox¬ 
ide of manganese and potash resulting from the decomposi¬ 
tion of the permanganate. 

If now we consider the various operations in the process, 
we shall find they consist of the following :— 

1. Dissolving the ore in an acid ; hydrochloric acid, for 
example. 

2. Treating the solution of the persalt of iron which 
results by sulphite of soda, to reduce it to the state of proto¬ 
salt, and to boil it in order to expel the excess of sulphurous 
acid.* 

3. Adding afterwards with precaution the solution of 
permanganate of potash until the pink tint appears, and 
then reading off on the graduated tube the number of 
divisions used. 

Now it will be perceived there are two conditions to ful¬ 
fil ; the first, to effect a complete reduction, for the persalts 


* As it is important to employ a sufficient quantity of the sulphite of soda to 
render the reduction of the persalt of iron to the state of protosalt complete 
and yet to leave sufficient hydrochloric acid in excess in the solution, it is 
advantageous to use a definite and known quantity. For this purpose 4 oz. of 
crystallised sulphite of soda are dissolved in a quart of water, and a pipette 
which contains 2 oz. is used to measure the quantity added to each assay. 87^ 
grs., which are contained in the 2 oz. of the pipette, are more than sufficient to 
reduce 20 grs. of iron; but this excess is necessary to ensure the entire reduc¬ 
tion of the persalt to protosalt. Metallic zinc is frequently used for this purpose 
and, according to Reynolds ( Chemical Neios, November 6 , 1864), sulphuretted 
hydrogen is preferable to both. Dr. Percy also recommends zinc. 



THE ASSAY OF IRON. 


271 


of iron do not react on the chameleon,—all that remained 
at the "maximum of oxidation will escape the action of the 
chameleon, and consequently will not be estimated as 
iron; the second, to expel by ebullition the whole of the 
sulphurous acid in excess, which, in contact with the per¬ 
manganate, would take from it the oxygen necessary to 
form sulphuric acid, and thus react in the same manner as 
the iron. But it is easily demonstrated by experiment, that 
the solution of a persalt of iron, treated with a sufficient 
quantity of sulphite of soda, is on the one hand completely 
reduced to its minimum of oxidation, and on the other hand 
does not contain the most minute trace of sulphurous acid 
after a few minutes’ ebullition. 

, A question here naturally presents itself, whether the 
salts of iron, reduced to their minimum, do not absorb 
oxygen again with great rapidity, and thus exert an influence 
on the results of the analysis: the following experiment, 
however, will remove all doubts on this head:—At this 
stage of the operation the solution was exposed to the 
contact of air for four hours, and the test-liquor then added ; 
a quantity of this was required exactly equal to that which 
was necessary when the analysis was prosecuted without any 
delay. This fact proves that the protosalts of iron in an 
acid solution are converted into persalts very slowly. 

It becomes important to ascertain whether, in the ores 
of iron there may not exist substances capable of reacting 
on the chameleon and thus rendering the estimation of the 
metal erroneous. 

On examining the composition of the greater number of 
the ores described by various authors, and particularly by 
MM. Berthier and Karsten, we find that they are most ordi¬ 
narily composed of the following substances :— 


Ores. 

r - A ; \ 

Iron. Phosphoric acid. 

Manganese. Lime. 

Zinc. Alumina. 

Arsenic. Magnesia. 

Copper. Silica. 


Metals. 

Cobalt. 

Nickel. 

Titanium. 

Chromium. 

Tungsten. 


The presence of zinc, manganese, titanium, tungsten, phos¬ 
phoric acid, lime, magnesia, alumina, and silica, do not at 




27 2 


ASSAY OF IRON IN T1IE WET WAY. 


all interfere with the accuracy of the results. Cobalt, nickel, 
and chromium, notwithstanding the peculiar colour of their 
solutions, do not in the least prevent the appreciation of the 
peculiar rose-pink tint of the mineral chameleon. 

Arsenic and copper, then, are the only substances 
among those capable of producing a discrepancy in the 
analysis ; as, under the influence of the sulphurous acid, the 
arsenic acid becomes arsenious acid, and the salts of per¬ 
oxide of copper become salts of the protoxide, and after¬ 
wards withdraw oxygen from the permanganate of potash. 

It is true that the ores containing arsenic are of little 
importance in a commercial point of view, for the iron pro¬ 
duced from them is of so inferior quality as to be generally 
rejected ; nevertheless, it has been considered right to give 
the method of analysis in cases where it occurs, and a slight 
modification of the general process is sufficient. 

The operation is carried on as usual, except that, after 
having boiled the solution to expel the excess of sulphurous 
acid, a piece of pure laminated zinc is added, which, acting 
upon the hydrochloric acid, disengages hydrogen; arsenic 
and copper are thereby reduced and precipitated in the 
metallic state. When the solution of the zinc is complete, 
the liquid is filtered from the precipitated particles of 
arsenic and copper, which would otherwise be re-oxidised ; 
and, after washing the filter three or four times with common 
water, the addition of the normal test-liquor is proceeded 
with. 

The method of preparing the permanganate of potash 
test-liquor has already been given in the chapter on Volu¬ 
metric Analysis. 

Permanganate of potash is a preparation of great sta¬ 
bility, and may be preserved for a very long time without 
undergoing any alteration, provided it be defended from the 
contact of organic matters and kept in a glass-stoppered 
bottle. To convert its solution into a test-liquor of known 
value, 20 grs. of pure iron, such as pianoforte wire, are 
dissolved in about 1 oz. of strong hydrochloric acid, free 
from iron ; after the disengagement of the hydrogen has 


ASSAY OF IRON IN THE WET WAY. 


273 


ceased, and the solution is complete, the liquid is diluted 
with about 1 pint of water.* 

The solution of permanganate of potash is then added, 
drop by drop, until a slight pink colour is manifest, and the 
number of divisions on the tube necessary to produce this 
effect carefully noted ; this number is then employed to 
reduce into weight the result of an analysis of an ore. 

When the solution of chameleon is too concentrated, it is 
easy, by adding the proper quantity of water, to reduce it 
to one-half, one-fourth, or one-fifth, so that 2 oz. shall be 
as nearly as possible equivalent to 20 grs. of iron. 

Freseniusy makes the following observations on the de¬ 
termination of iron in hydrochloric acid solution by the 
foregoing method. This process was long considered 
to be the most convenient and best for the estimation of 
iron. But its glory is now departed, since Lowenthal and 
Lenssen have shown that in solutions containing hydrochlo¬ 
ric acid, it is essential that the standardising of the reagent 
and the actual analysis be performed under the same circum¬ 
stances *as regards dilution, amount of acid, and tempera¬ 
ture. Besides the proper reaction, 10FeO + Mn 2 O 7 = 5Fe 2 O 3 
2Mn 0, the collateral reaction 7I1C1 +- Mn 2 0 7 = 5C1 + 2MnCl + 
7IIO also takes place, in consequence of which a little chlo¬ 
rine is liberated. This chlorine does not oxidise the prot¬ 
oxide of iron in the case of considerable dilution, but there 
occurs a condition of equilibrium in the fluid containing 
protoxide of iron, chlorine, and hydrochloric acid, which is 
destroyed by addition of a further quantity of either body 
(Lowenthal and Lenssen). But since it is difficult to pre¬ 
serve the above condition of obtaining correct results, the 
following proceeding is adopted. 

4 Standardise the permanganate by means of iron dissolved 
in dilute sulphuric acid, make the iron solution to be tested 
up to j litre, add 50 c.c. to a large quantity of water acidi¬ 
fied with sulphuric acid, add permanganate from burette, 
then again 50 c.c. of the iron solution,permanganate again, &c. 

* It is necessary to use solutions very dilute and cold, in order to prevent 
the hydrochloric acid in excess from reacting on the chameleon and disengaging 
chlorine. 

t Fresenius’s Quantitative Analysis, 4th edition, p. 191. 

T 


274 


ASSAY OF IKON IN THE WET WAY. 


&c. The numbers obtained at the third and fourth time are 
taken. These are constant, while that obtained the first 
time, and sometimes also the second time, differs. The 
result multiplied by 5 gives exactly the quantity of perman¬ 
ganate proportional to the amount of protoxide of iron 
present. 

4 1 believe that the reason why the attention of analysts 
was not previously directed to the important influence of 
hydrochloric acid in this process, lay in the fact that it was 
not customary to crystallise the permanganate before em¬ 
ploying it—the crude solution, which contains much chlo¬ 
ride of potassium, being used. The experiments were con¬ 
sequently performed in the presence of free hydrochloric 
acid, even when sulphuric acid alone was employed for 
dissolving or acidifying. Hence the differences between the 
results with sulphuric and hydrochloric acid solutions were 
not so large as they are now, when we work with the pure 
permanganate.’ 

In reference to this process, Mr. J. P. Blunt has commu¬ 
nicated the following observations to the 4 Chemical News.’ 

4 In the course of some late experiments on the estimation 
of the value of iron ore by means of permanganate of potash, 
I met with much annoyance from the inconstancy of the 
results obtained. The reducing agent used was metallic 
zinc, and the ore, being a very rich protosesquioxide con¬ 
taining nearly 65 per cent, of iron, required a large quantity 
of hydrochloric acid for its decomposition, and a correspond¬ 
ing amount of zinc for its reduction. My first suspicions 
fell upon the zinc, and I accordingly dissolved a little of it 
in hydrochloric acid, and, when the solution was quite com¬ 
plete, added a few drops of the permanganate solution ; the 
colour immediately disappeared, and a strong and unmistake- 
able odour of chlorine was evolved. This led me to con¬ 
clude that my failures had arisen from an insufficient dilu¬ 
tion of the hydrochloric acid used, and I determined to 
institute experiments with the object of discovering what 
amount of dilution was necessary in order to prevent the 
decomposition of permanganate of potash by hydrochloric 
acid. The results of these experiments I now submit, as I 


DR. PENNY’S PROCESS. 


275 


believe that it is not generally known that any but the 
strongest solutions of hydrochloric acid have such an effect, 
and a knowledge of this may preserve those engaged in 
similar inquiries from the vexation and perplexity to which 
I have been subjected. 

6 Nine solutions of hydrochloric acid were prepared of 
successive degrees of dilution. No. 1, containing 1 part 
of hydrochloric acid, of 1*45 specific gravity, to 1 part of 
water. No. 9, containing 1 part of the same acid to 9 of 
water. Three or four drops of the permanganate solution 
were mixed with each ; the results were as follows :— 

4 No. 1. The colour disappeared immediately. 

4 No. 2. The colour disappeared in one or two seconds. 

4 No. 3. The colour disappeared in about half a minute. 

4 No. 4. The colour disappeared in one minute and a half. 

4 No. 5. The colour disappeared in about six minutes. 

4 No. 6. Just coloured after nine minutes. 

4 No. 7. Eetains its colour for nearly a quarter of an hour, 
but smells strongly of chlorine after about a minute. . 

4 No. 8. Smells of chlorine after about two minutes. 

4 No. 9. Smells very faintly after three minutes. 

4 In inspecting these results it should not be forgotten that 
a dilute solution of permanganic acid, such as that formed 
in the experiments, decomposes spontaneously in a short 
time, and this presents oxygen in a nascent state eminently 
fitted for the decomposition of hydrochloric acid ; it is pro¬ 
bable that the smell of chlorine in experiments No. 6, 7, 8, 
and 9, may be partially attributed to this, but there would be 
great danger of the faint colour—which is sufficient to the 
practised eye to show the completion of the process of esti¬ 
mation—being destroyed by such a solution as No. 5, and as 
drop after drop was added, the same action would continue, 
and would seriously vitiate the results.’ 

Dr. Penny s Process. —The following method of determining 
the amount of iron in a sample by means of a normal solu¬ 
tion, has been contrived by Dr. F. Penny, who was led to 
substitute bichromate of potash for permanganate of potash, 
as recommended by Marguerite, and just described. The 
reason of employing the bichromate is, that it is an uncliange- 



276 


ASSAY OF IRON IN TIIE WET WAY. 


able salt, whilst the permanganate sometimes undergoes 
decomposition, so that its strength is variable, and each 
series of experiments made with it requires a separate veri¬ 
fication by means of a weighed quantity of pure iron. This 
inconvenience is avoided in Dr. Penny’s method, which is 
described in his own words as under :— 

4 In the first series of experiments, pure harpsichord wire 
was dissolved with every care in hydrochloric acid, and 
bichromate of potash, added to the solution until the con¬ 
version of the protochloride of iron into the perchloride was 
complete. I obtained the following results : 


1 Exp. 


V 

V 
)) 


Iron. Bichromate. 

I. 60 grains required 44-4 grains. 

II. 39-7 „ „ 35-2 

III. 48*3 „ „ 42-8 

IV. 65-3 „ „ 49-2 


)) 

v 


4 The mean of these results is, 100 parts of iron to 88*75 
of bichromate. 

4 In the second series of experiments protosulphate of 
iron was employed. This salt was made from protosulphide 
of iron, and purified most carefully by repeated crystal¬ 
lisation. A known quantity of it was dissolved in water, 
acidulated with either pure hydrochloric or sulphuric acid, 
and the solution treated with bichromate :— 


1 Exp. 


V 

V 
)) 


I 

II. 

III. 

IV. 


Sulphate of Iron. 


Bichromate. 


100 grains required 17-90 grains. 
180 „ „ 3210 

150 „ „ 2082 

120 „ „ 21-40 


V 

)) 


V 


V 


4 These experiments give the ratio of 100 parts of sul¬ 
phate of iron to 17*867 of bichromate, or 100 of iron to 
88*71, which corresponds very closely to the mean result 
obtained with the metallic iron. Moreover, I performed a 
series of similar experiments with the neutral chromate of 
potash, and obtained results completely confirmatory of the 
general accuracy of the foregoing experiments. We may, 
therefore, I think, safely conclude that 100 parts of metallic 
iron correspond to 88*75 of the bichromate of potash, and 
that 100 of the latter are equal to 112*67 of the former. 

4 1 shall now proceed to describe the method of employ¬ 
ing the bichromate of potash for the determination of the 



DR. PENNY’S PROCESS. 


277 


amount of iron in clay-band and black-band ironstone. I 
shall be purposely minute, as I particularly desire that the 
process may be serviceable to those who, from their pursuits 
in life, are interested in the value and quality of ironstone, 
and who may be imperfectly acquainted with analytical ope¬ 
rations. 

A convenient quantity of the specimen is reduced to 
coarse powder, and one-half at least of this still further pul¬ 
verised, until it is no longer gritty between the fingers. The 
test solution of bichromate of potash is next prepared. 44*4 
grs. of the salt in fine powder are weighed out, and put into 
an alkalimeter (graduated into 100 equal divisions), and 
tepid distilled water afterwards poured in until the instru¬ 
ment is filled to 0. The palm of the hand is then securely 
placed on the top, and the contents agitated by repeatedly 
inverting the instrument, until the salt is dissolved and the 
solution rendered of uniform density throughout. It is 
obvious that each division of the solution thus prepared 
contains 0'444 gr. of bichromate, which corresponds to ^ a 
grain of metallic iron. The bichromate of potash used for 
this process must of course be purchased pure, or made so 
by repeated crystallisation, and it should be thoroughly 
dried by being heated to incipient fusion. 

6 100 grs. of the pulverised ironstone are now introduced 
into a Florence flask, with li oz. by measure of strong 
hydrochloric acid, and \ an ounce of distilled water. Heat 
is cautiously applied, and the mixture occasionally agitated, 
until the effervescence caused by the escape of the carbonic 
acid ceases ; the heat is then increased, and the mixture made 
to boil, and kept at moderate ebullition for ten minutes 
or a quarter of an hour. During these operations it will be 
advisable to incline the flask, in order to avoid the projec¬ 
tion, and consequent loss, of any portion of the liquid by 
spirting. About 6 oz. of water are next added, and mixed 
with the contents of the flask, and the whole rapidly trans¬ 
ferred to an evaporating basin. The flask is rinsed several 
times with water, to remove all adhering solution. 

‘ Several small portions of a weak solution of pure red 
prussiate of potash (containing one part of the salt to 40 of 


278 


ASSAY OF IKON IN TIIE WET WAY. 


water) are now dropped upon a white porcelain slab, which 
is conveniently placed for testing the solution in the basin 
during the next operation. 

4 The prepared solution of bichromate of potash in the 
alkalimeter is then added very cautiously to the solution of 
iron, which must be repeatedly stirred, and as soon as it 
assumes a dark greenish shade, it should be occasionally 
tested with the red prussiate of potash. This may be easily 
done by taking out a small quantity on the top of a glass 
rod, and mixing it with a drop of the solution on a porcelain 
slab. When it is noticed that the last drop communicates 
a distinct red tinge, the operation is terminated. The alkali- 
meter is allowed to drain for a few minutes, and the number 
of divisions in the test-liquor consumed read off. This num¬ 
ber multiplied by two gives the amount of iron per cent, in 
the specimen of iron-stone, assuming that, as directed, 100 
grs. have been used for the experiment. The necessary 
calculation for ascertaining the corresponding quantity of 
protoxide is obvious. 

4 When black-band ironstone is the subject of analysis, 
or when the ore affords indications, by its appearance or 
during the treatment with hydrochloric acid, that it contains 
an appreciable quantity of carbonaceous matter, then the 
hydrochloric acid solution must be filtered before being 
transferred to the basin, and the filter, with the insoluble 
ingredients must be washed in the usual way with warm 
distilled water, slightly acidulated with hydrochloric acid 
until the filtrate ceases to give a blue colour with the red 
prussiate of potash. In those cases, also, where the presence 
of iron pyrites in the ironstone is suspected, it will be neces¬ 
sary to remove the insoluble matter by filtering before 
applying the bichromate solution ; but with ironstones in 
which the insoluble ingredients are merely clay and silica, 
filtration is not essential. 

4 Now it is evident that the foregoing process, so far as 1 
have described it, serves for the determination of that portion 
of iron only which exists in the ore in the state of protoxide. 
But many specimens of the common ironstone of this country 
contain appreciable quantities of peroxide of iron, which, 


DR. PENNY’S PROCESS. 


279 


being unacted upon by the bichromate of potash, would 
escape estimation by the present method. By an addition 
and easy operation, however, the amount of metallic iron in 
this ingredient may be likewise determined. It is only 
necessary to reduce it to the minimum state of oxidation 
and then to add the bichromate as previously directed. 

4 The best and most convenient agent for effecting the 
reduction of the persalts of iron is sulphite of soda. The 
only precaution to be observed is to use it in sufficient quan¬ 
tity, and at the same time to take care that the iron solution 
contains excess of acid. When the reduction is complete, a 
few minutes’ ebullition suffices to decompose the excess of 
sulphite of soda, and effectually to expel every trace of sul¬ 
phurous acid. 

4 In order to test the exactness of this mode of estimating 
the iron of the peroxide, I made several experiments with 
peroxide prepared from known quantities of pure iron wire. 
The peroxide was thoroughly washed, dissolved in hydro¬ 
chloric acid, reduced with sulphite of soda, and after com¬ 
plete expulsion of the excess of sulphurous acid, the solution 
was diluted with water and treated with bichromate of 
potash. I select three of the experiments :— 

1 Exp. I. 10 grains of iron consumed 8*87 of bichromate. 

„ II. 18 „ „ „ 15-94 

„ III. 25 „ „ „ 22-15 

4 The mean of all my experiments on this point gives the 
ratio of 100 of iron to 88*6 of bichromate, which is in close 
accordance with the former results. 

4 Whenever, therefore, the ore of iron contains peroxide 
it will be necessary to add sulphite of soda to the hydrochlo¬ 
ric acid solution before the addition of the test-liquor from 
the alkalimeter. The sulphite should be dissolved in dis¬ 
tilled water, and added to the solution of iron in small 
successive portions, until a drop of the liquor gives merely 
a rose-pink colour with sulphocyanide of potassium, which 
indicates that the reduction of the persalt of iron is suffi¬ 
ciently perfect. The liquor is now heated till the odour of 
sulphurous acid is no longer perceptible. These operations 


280 


ASSAY OF IRON IN TIIE WET WAY. 


should be performed while the solution is in the flask, and 
before it is Altered or transmitted to the basin. 

4 1 will here mention for the guidance of those who may 
not be fully aware of the reactions of the oxides of iron, that 
the existence of an appreciable quantity of peroxide in the 
ironstone may be readily discovered by dissolving (as 
directed in the process) 39 or 40 grs. of the ore in hydro¬ 
chloric acid, diluting with about 8 oz. of water, filtering and 
testing a portion of the solution with sulphocyanide of potas¬ 
sium. If a decided dark blood-red colour is produced, the 
quantity of peroxide in the stone must be determined ; but 
if the colour is only light red or rose-pink, the proportion is 
exceedingly small, and for practical purposes not worth esti¬ 
mating. Of course, when the specimen of ironstone has an 
ochrey or a reddish appearance on the surface or in the 
fracture, the presence of a large proportion of peroxide is 
indicated, and its exact quantity must be determined. 

4 In conclusion, I must not omit to notice one or two 
circumstances which appear at first to militate against the 
accuracy of this process. It may be questioned whether 
solutions of the protosalts of iron do not absorb oxygen so 
rapidly from the air as to influence the results obtained by 
this method. Marguerite has shown (see ante), and my own 
observations completely confirm his statement, that protosalts 
of iron, in an acid solution, become peroxidised very slowly ; 
and, in a particular experiment, I found that contact with 
the air during several hours caused no diminution in the 
quantity of bichromate of potash required. As the process 
may be completed in a few minutes, it is certain that no 
inaccuracy can arise from this cause. 

4 It is also important to inquire whether the chromic acid 
in the chromates of potash may not be partially deoxidised 
by hydrochloric acid alone without the presence of a proto¬ 
salt of iron. Such a reaction would obviously give rise to 
a serious error. It is well known that concentrated hydro¬ 
chloric acid rapidly decomposes the chromic acid of the 
chromates when aided by the application of heat. But I 
have satisfied myself, by numerous experiments, that this 
acid exerts very little appreciable action upon dilute solutions 


m. mittenzwey’s teocess. 


281 


of the chromates of potash, either cold or warm, and that 
the action is only partial even after continued ebullition ; 
so that the present method is free from inaccuracy on this 
account.’ 

M. Mittenzwey's Process. —M. Moritz Mittenzwey has 
described a very good process for estimating iron by means 
ol tannic acid. The estimation can be conveniently made 
in the simple apparatus here figured and described. 

The air in a bottle, a, fig. 76, capable of holding about a 
litre and a half, communicates with the 
atmosphere by the bent tubes, b and c, the 
latter being drawn out at the end d to the 
diameter of about one or one and a half 
millimetres. The two glass tubes are 
united by means of a moderately long 
piece of india-rubber tubing, E, provided 
with a pinchcock, F, to close it; and the 
lower glass tube is fixed in the neck of 
the bottle by a bored cork, or, better, 
a caoutchouc stopper. 

In executing the analysis it is abso¬ 
lutely necessary that the air in the bottle should be 
perfectly renewed, and the temperature of all reaching 
the fluid be the same as that of the laboratory. As soon 
as the absorbing liquid (which should amount to 150 or 
250 c.c.) is prepared, the bottle should be perfectly closed, 
and then the pinchcock opened just for a moment, so 
that the pressure of the internal and external air may 


Fig. 76. 



Fig. 77. 



be equalised. The absorption of the oxygen is then 
hastened by strongly shaking the bottle, which must be 
wrapped in a cloth to avoid raising the temperature by the 
warmth of the hand. After each shaking, water must be 
















282 


ASSAY OF IRON IN TIIE WET WAY 


allowed to flow into the bottle, A, from a weighed quantity in 
a beaker, B, fig. 77, so that the fluid in the two vessels may 
attain the same level, as shown in the drawing. The experi¬ 
ment is ended when, after repeated shakings, no more water 
runs from B to A, and the difference in the weight of the 
water in the beaker in grammes gives the amount of oxygen 
absorbed in cubic centimetres, which can be corrected for 
the standard temperature and pressure. 

In order to apply this to the estimation of iron compounds 
these must be reduced to the state of protoxide by means of 
zinc, and the excess of acid neutralised with caustic potash 
or soda. (Ammonia and the carbonated alkalis must be 
avoided.) The solution is then poured into the absorption- 
flask, and pieces of potash wrapped in paper are then dropped 
in. The absorption is complete in a very short time. For 
accuracy this process is second to none, and may be recom¬ 
mended in preference to that of Marguerite and Fuchs, 
since it requires fewer precautions. 50 c.c. of a solution of 
protoxide which contained 1*395 Fe absorbed in three 
experiments 148*0 c.c., 148*44 c.c., and 148*4 c.c. of oxygen 
at 19° C.; the mean = 148*28 c.c., which at this tempera¬ 
ture weigh 0*1987 gramme, answering in 1*391 grammes of 
iron. 

4. Titration of Iron by Protocliloride of Tin. —Mr. Sutton, 
in his excellent 4 Volumetric Analysis ’ before quoted, gives 
the following directions for the direct titration of iron by 
protochloride of tin. 

The principle involved in this reaction is, in fact, simply 
a reversion of the ordinary process by permanganate and 
bichromate. In the case of these two reagents, the amount 
of oxygen given up by them is the measure of the quantity 
of iron, whereas with protochloride of tin, it is the amount 
taken up by it that answers the same purpose. 

Fresenius (in his 4 Zeitschrift fur Analytische Chemie,’ 
part 1, page 26) has recorded a series of experiments made 
on the weak points of this process, and gives it as his opinion 
that it is most accurate and reliable with proper care, with¬ 
out which, of course, no analytical process whatever is 
worth anything. The summary of his paper is as follows :_ 


ASSAY OF IRON IN THE WET WAY. 


283 


a. A solution of peroxide of iron of known strength is 
first prepared, by dissolving 10-03 grm. fine pianoforte wire 
( = 10 grm. pure iron) in pure hydrochloric acid, adding 
chlorate of potash to complete oxidation; boiling till the 
excess of chlorine is removed, and diluting the solution to 
1 litre. 

b. A clear solution of protochloride of tin, of such strength 
that about equal volumes of it and the iron solution are 
required for the complete reaction. 

c. A solution of iodine in iodide of potassium, containing 
about 0’005 grm. iodine in 1 c.c. (if the operator has the 
ordinary decinormal iodine solution at hand, it is equally 
applicable.) The operations are as follows : 

1. 1 or 2 c.c. of the tin solution are put into a beaker 
with a little starch liquor, and the iodine solution added 
from a burette till the blue colour occurs ; the quantity is 
recorded. 

2. 10 c.c. of the iron solution = 0T grm. iron, are put into 
a small flask with a little hydrochloric acid, and heated to 
gentle boiling (preferably on a hot plate), the tin solution 
is then allowed to flow in from a burette until the yellow 
colour of the solution is nearly destroyed, it is then added 
drop by drop, waiting after each addition until the colour is 
completely gone and the reduction ended. If this is care¬ 
fully managed there need be no more tin solution added 
than is actually required ; however, to guard against any 
error in this respect, the solution is cooled, a little starch 
liquor added, and the iodine solution added by drops until 
a permanent blue colour is obtained. As the strength of 
the iodine solution compared with the tin has been found in 
1, the excess of tin solution corresponding to the quantity 
used is deducted from the original quantity, so that by this 
means the volume of tin solution corresponding to 0*1 grm. 
iron is found. 

The operator is, therefore, now in a position to estimate 
any unknown quantity of iron which may exist, in a given 
solution, in the state of peroxide, by means of the solution of 
tin. 

If the iron should exist partly or wholly in the state of 


284 


ASSAY OF IRON IN THE WET WAY. 


protoxide, it must be oxidised by the addition of chlorate of 
potash, and boiling to dissipate the excess of chlorine, as 
described in 2. 

Example : 10 c.c. of iron solution, containing 0'1 grm. iron, 
required 15 c.c. of tin solution. 

A solution, containing an unknown quantity of iron, was 
then taken for analysis, which required 12 c.c., consequently, 
a rule of three sum gave the proportion of iron as follows :— 

15 : 0T grm. :: 12 : 0*08 grm. 

It must be remembered that the solution of tin is not 
permanent, consequently it must be tested every day afresh. 
Two conditions are necessary in order to ensure accurate 
results. 

1st. The iron solution must be tolerably concentrated, 
since the end of the reduction by loss of colour is more 
distinct; and, further, the dilution of the liquid to any 
extent interferes with the quantity of tin solution necessary 
to effect the reduction. Fresenius found that by diluting the 
10 c.c. of iron solution with 30 c.c. of distilled water, y 1 ^ of 
a c.c. more was required than in the concentrated state. 
This is, however, always the case with protochloride of tin 
in acid solution, and constitutes the weak point in Streng’s 
method of analysis by its means; it would seem that dilu¬ 
tion either predisposed it to rapid oxidation, or that water 
had the power within itself to communicate a certain pro¬ 
portion of oxygen to it. 

2nd. The addition of the tin solution to the iron must be 
so regulated that only a very small quantity of iodine is 
necessary to estimate the excess—if this is not done another 
source of error steps in, namely the influence which dilution, 
on the one hand, or the presence of great or small quantities 
of hydrochloric acid on the other, are known to exercise 
over this reaction ; practically it was found that where the 
addition of tin, to the somewhat concentrated iron solu¬ 
tion, was cautiously made so that the colour was just dis¬ 
charged, the mixture then rapidly cooled, starch added, and 
iodine till blue, that the estimation was as reliable as by any 
other method. 


DETERMINATION OF ALL THE CONSTITUENTS. 


285 


The following examples are from Fresenius. 

The standard iron solution contained 10 grm. in the litre ; 
10 c.c. were therefore equal to 0T grm. iron. 1 c.c. tin 
solution required 3-62 c.c. iodine. 

Exp. 1. 9*97 c.c. of the above iron solution required 

11*6 c.c. tin solution and 1*23 c.c. iodine. 

Exp. 2. 9*87 c.c. iron solution required 11*26 c.c. tin and 
0*44 c.c. iodine. Calculated for 0T grm. iron, the above 
experiments show that— 


1 = 11 294 c.c. tin solution 

2 = 11-287 
Mean 11-2905 


v 

v 


v 


3-8204 grm. brown haematite ore was heated with concen¬ 
trated hydrochloric acid until decomposed, then diluted 
somewhat, filtered, and the solution made up to 500 c.c. 

Exp. 1. 100 c.c. required 43'69 c.c. tin solution and 

0-26 c.c. iodine. 

Exp. 2. 100 c.c. required 4415 c.c. tin and 2*12 c.c. 
iodine, therefore,— 

1 = 43-62 c.c. tin solution 

2 = 43-57 

Mean 43-60 


ft 


ff 

ff 


The following equation expresses the result. 

11-2905 SnCl : 0T Fe :: 43*60 : #=0*3862 grm. iron in 
100 c. c. or 50-54 per cent, of iron in the ore. 

A determination of the iron, in the same sample of ore, by 
permanganate, executed with the greatest care, gave 50*58 
per cent. 

The tin solution is best prepared by placing fragments of 
pure tin at the bottom of a beaker, laying a small platinum 
crucible or cover upon them, and covering the whole with 
equal parts of pure hydrochloric acid and water: a large 
watch-glass or porcelain capsule should be placed on the 
top of the beaker, to exclude air and prevent loss by spirting. 

The contact of the platinum with the tin sets up a galvanic 
current which materially hastens the solution of the tin 
without at all affecting the platinum; when the acid is all 
saturated, it may be poured off and fresh added until sufficient 
solution has been obtained. The whole, freely acidified and 


286 


ASSAY OF IRON IN THE WET WAY. 


diluted to a convenient strength, should be placed in a well- 
stoppered bottle, with a few fragments of tin; its strength, 
which is constantly lessening to a slight extent, must be 
found before using it. 

Quantitative Determination of all the Constituents usually 
present in an Iron Ore. —The ordinary constituents of clay 
ironstone (which is about the most complex, and the detail 
of whose analysis will be the most useful) are the per- and 
protoxides of iron, oxide of manganese, alumina, magnesia, 
lime, potash, soda, sulphur, phosphoric acid, carbonic acid, 
silica, and water. 

Some iron ores dissolve very readily in hydrochloric acid 
or in aqua regia ; others do not, even when they are in a 
very fine state of division; but all do readily after fusion 
with an alkah, or an alkaline carbonate,—as of potash or 
soda, hence it is advisable to fuse the finely pulverised ore 
with an alkali previous to attempting its solution in an acid. 

In determining the amount of iron, the author recom¬ 
mends Dr. Penny’s process. 

Determination of Silica , Oxide of Iron , and Oxide of Man¬ 
ganese. —The ore must be reduced to the finest possible 
state of division, a small quantity placed in a test-tube, and 
boiled for some time with hydrochloric acid. If it com¬ 
pletely decomposes it need not be submitted to fusion with 
carbonate of soda, but 100 grains may be at once weighed 
off, and treated in a Florence flask with about 2 ounces of 
hydrochloric acid, gradually heated to ebullition, and that 
temperature maintained until perfect decomposition has 
ensued. If, on the other hand, the ore does not completely 
decompose, 100 grains must be carefully mixed with 500 or 
600 grains of carbonate of soda placed in a platinum cruci¬ 
ble and fused at a bright red heat; the fusion must continue 
about half an hour. It may be here mentioned that the 
platinum crucible, previous to its introduction into the furnace, 
must be placed in one of clay furnished with a cover, to 
protect it from the injurious effect of contact with the fuel. 

When the platinum crucible and its contents are cold, it 
is placed in a large evaporating basin, and pure dilute hy¬ 
drochloric acid poured over it: the fused mass dissolves 


ASSAY OP IRON IN TIIE WET WAY. 


287 


with effervescence, and more acid must be gradually added 
as seems necessary, until no further action takes place. The 
solution being finished, the crucible is removed, washed 
with distilled water, and the whole, together with the wash¬ 
ings, evaporated to dryness. The solution obtained in the 
first case, in which the ore was wholly decomposable by hy¬ 
drochloric acid alone, is also to be evaporated to dryness. 
The object of this evaporation is the conversion of the silica 
the ore may contain from a partially soluble to a completely 
insoluble state, so that the whole of it may be collected and 
weighed. 

Towards the end of the operation, the partially-dried mass 
must be continually stirred, in order to prevent losses by the 
spirting which will otherwise take place. When cold, the 
contents of the basin are moistened Fig. 78. 

with hydrochloric acid, and the 
whole left to itself for about one 
hour. It is then mixed with a small 
quantity of distilled water, gently 
warmed and thrown upon a filter. 

Every constituent of the ore, with 
the exception of the silica, will pass 
through the filter in a liquid state. 

The silica remaining in the filter is 
to be well washed with hot water, 
dried,* ignited in a platinum cruci¬ 
ble, and weighed. 

To the liquid filtered from the 
silica and with which the washings have been incorporated 
add a few drops of nitric acid, and boil; when cool, add 
gradually pure precipitated carbonate of baryta until in 
excess, which point may be ascertained by cessation of effer¬ 
vescence, and by some of the carbonate remaining undis¬ 
solved. The whole is now to be kept at a gentle heat for 
about an hour, and then poured on a filter, in which will re- 

* The most convenient form of apparatus for drying precipitates, filters, &c. 
in analysis, is a little water-oven, called a ( water-bath ’ (see fig. 78). It con¬ 
sists of a double box of copper or tin plate about six inches square, with water 
between the casings, which is kept in a state of ebullition by means of a gas 
flame or spirit lamp. 

































288 


ASSAY OF IRON ORE. 


main the peroxide of iron, alumina, and phosphoric acid, 
together with the excess of carbonate of baryta employed. 
The liquid which has passed through the filter is mixed with 
excess of sulphide of ammonium, covered with a glass plate 
to exclude air, and left to itself for four or five hours. If 
any manganese were present in the ore, it will now be 
thrown down as a flesh-red precipitate, which must be col¬ 
lected on a filter, washed, dissolved in a small quantity of 
hydrochloric acid, the solution filtered, and excess of carbo¬ 
nate of soda added : carbonate of manganese is precipitated, 
which is collected on a filter, washed, dried, ignited and 
weighed as red oxide, every 100 parts of which correspond 
to 93 parts of the protoxide of manganese, in which state it 
usually exists in the ore. The weight so obtained gives 
the percentage. The mixed precipitate of oxide of iron, 
alumina, carbonate of baryta, and phosphoric acid remaining 
on the filter, is dissolved in a small quantity of hydrochloric 
acid, and the amount of iron ascertained by Dr. Penny’s 
process, as already described. As the iron is in the state of 
peroxide, its reduction to protoxide must be effected by 
sulphite of soda, according to the method already given. 

Determination of Lime and Magnesia , and part of Phos¬ 
phoric Acid. —Dissolve another 100 grains of ore with the 
precautions already pointed out, only in this case the silica 
may be rejected, and treat the solution by the following 
process, which was contrived by Fresenius :— 

The solution is heated to ebullition in a flask, and reduced 
with sulphite of soda, then precipitated with carbonate of 
soda, and boiled with excess of caustic soda until the preci¬ 
pitate appears black and granular. It is allowed to subside, 
the clear liquid poured off, the precipitate washed by de¬ 
cantation with hot water, and finally brought upon a filter 
of close texture and washed with hot water. 

Treatment of the Precipitate. —The precipitate is again 
transferred, together with the filter, into the flask, and di¬ 
gested with hydrochloric acid. When no more black par¬ 
ticles are perceptible it is filtered ; the filter is left whole, a 
little water poured over it, and the flask inclined so that it 
remains hanging by the side while the liquid runs off: in 




289 


ASSAY OF IRON ORE. 

this manner it may be quickly and completely washed. The 
filtered solution is reduced with sulphite of soda, heated to 
boiling, mixed with a few drops of chlorine water, then 
with an excess of acetate of soda ; and when the liquid or 
precipitate has not a reddish tint, chlorine water is added 
until this is the case. The whole is boiled until the precipi¬ 
tate has separated, filtered hot, and the precipitate, consist¬ 
ing of phosphate and some basic acetate of the peroxide of 
iron, washed. 

To the solution just filtered from the phosphate of iron, 
add ammonia and sulphide of ammonium, and filter while 
hot; this removes manganese and iron, leaving lime and 
magnesia alone in solution. The whole is filtered while 
hot, and the precipitate remaining on the filter rejected. 
To the filtered solution is.added excess of solution of oxalate 
of ammonia : this throws down insoluble oxalate of lime, 
which must be collected on a filter, washed, dried, and ig¬ 
nited at a low red heat. The residue is now carbonate of 
lime, every 100 parts of which correspond to 56*29 parts of 
lime. 

To the solution filtered from the oxalate of lime, and 
which contains the magnesia, add excess of phosphate of 
soda, agitate briskly, and set aside for twelve hours ; then 
collect the crystalline precipitate of ammonio-phosphate of 
magnesia on a filter, wash it with water containing a little 
ammonia, dry and ignite it; weigh the resulting pyro-phos- 
phate of magnesia: every 100 parts correspond to 36*67 
parts of magnesia. 

The precipitate containing the perphosphate and basic 
acetate of soda is dissolved in hydrochloric acid, reduced 
with sulphite of soda, boiled for some time with excess of 
caustic soda, and filtered. The filtered solution which con¬ 
tains the phosphoric acid is supersaturated with hydrochloric 
acid, and placed aside for future operation. 

Treatment of the alkaline solution 'poured off from the first 
black precipitate. Determination of Alumina and remainder 
of Phosphoric Acid. —The solution is acidulated with hydro¬ 
chloric acid, a little chlorate of potash added, and then 
boiled; it is then precipitated with ammonia (avoiding a 




200 


ASSAY OF IRON ORE. 

large excess), and chloride of barium added as long as a 
precipitate appears. After digesting for some time it is 
filtered. The precipitate, which contains the whole of the 
alumina and phosphoric acid, is collected on a filter, washed 
with a little water, and dissolved in as little hydrochloric 
acid as possible. The solution is saturated with precipitated 
carbonate of baryta, gently warming ; an excess of caustic 
soda is added, and the heat still kept up. Any baryta con¬ 
tained in the solution is removed by carbonate of soda, 
which is added until no further precipitation takes place. 
The whole of the alumina is now in solution, and the whole 
of the phosphoric acid in the precipitate. 

The solution is rendered acid with a little hydrochloric 
acid, boiled with a small quantity of chlorate of potash, 
precipitated with excess of ammonia, and allowed to stand 
for a few hours ; after which the precqntated alumina is 
collected on a filter, washed, dried, ignited, and weighed: 
its amount represents the per-centage of alumina in the ore. 

The precipitate containing the phosphoric acid is dissolved 
in hydrochloric acid, the baryta precipitated with dilute sul¬ 
phuric acid, which is added until no further precipitate 
ensues ; the liquid and precipitate placed in a warm situa¬ 
tion until the former is quite bright: it is then filtered, and 
to the filtered liquid is added the small portion reserved, as 
before directed : excess of ammonia is added to the mixture, 
then some-chloride of ammonium, and lastly sulphate of mag¬ 
nesia. The phosphoric acid is precipitated as the ammo- 
nio-phosphate of magnesia, which is washed, dried, and 
ignited, with the precautions already pointed out. Every 
100 parts correspond to 63-33 parts of phosphoric acid. 

Determination of Potash and Soda .—If the ore be com¬ 
pletely decomposible by hydrochloric acid, dissolve at once 
100 grains in that liquid ; if not, fuse the same quantity with 
four times its weight of hydrate of baryta in a platinum cru¬ 
cible : treat with hydrochloric acid, and separate the silica 
precisely as already described. To the filtered solution add 
an excess of baryta water ; this precipitates everything but 
the potash and soda and part of the lime. Throw tlie whole 
on a filter, well wash the precipitate, and add the washings 


ASSAY OF IRON ORE. 


291 


to the bulk of the filtered liquid ; to which add excess of 
ammonia and carbonate of ammonia : by these reagents the 
small quantity of lime and the excess of baryta in solution 
are precipitated. The solution must now be filtered, evapo¬ 
rated to dryness, and ignited. The dry residue consists of 
chlorides of potassium and sodium, which must be weighed, 
then dissolved in water to which a little hydrochloric acid 
is added, then excess of chloride of platinum, and the whole 
evaporated to dryness in the water bath; alcohol is now 
added, and the whole thrown on a small filter. The yellow 
precipitate of platino-chloride of potassium on the filter is 
washed with alcohol until the latter passes off colourless. 
The filter and its contents are then dried and weighed. 
Every 100 parts of platino-chloride of potassium correspond 
to 30*56 parts of chloride of potassium. The quantity of 
chloride of potassium thus obtained is deducted from the 
weight of the mixed chlorides of sodium and potassium as 
obtained above; the difference will be the amount of chlo¬ 
ride of sodium. Every 100 parts of chloride of sodium 
correspond to 53*28 of soda, and every 100 parts of chloride 
of potassium to 63*25 of potash. 

Determination of Sulphur .—Dissolve 100 grains of the ore 
in either of the manners already described, separating the 
silica ; in this case, however, a little nitric acid must be added 
to the hydrochloric acid previous to its mixture with the 
ore. To the filtered solution, made somewhat dilute, add 
excess of chloride of barium, and allow to stand in a warm 
place for a few hours. Collect the precipitate of sulphate of 
baryta on a filter, wash, dry, ignite, and weigh. Every 100 
parts correspond to 13*79 parts of sulphur. 

Determination of Carbonic Acid .—The most convenient 
apparatus for the determination of this gas is that invented 
by Eresenius and Will, of which the following is a descrip¬ 
tion. Fig. 7 9 shows its construction. A is a large flask of 
about two ounces capacity, in which the decomposition of 
the carbonate is effected : B a somewhat smaller flask, con¬ 
taining strong sulphuric acid : both are supplied with doubly 
pierced corks, for the reception of the three tubes a, c, 
and d. The tube a is confined to the flask A , being im- 



202 


ASSAY OF IKON ORE. 




mersed below the level of the fluid : in the same manner, cl is 
only connected with the flask I>, and only extends just 

below the cork. Lastly, the tube c 
Fig. 79 . enters the neck of A on the one side, 

but does not extend further, and, 
by a double bend, is brought into 
connection with B , which it enters, 
dipping into the sulphuric acid. 
The mouth of a is closed with wax 
during the experiment, so that no 
orifice is left in the whole appara¬ 
tus but the mouth of the tube d. 

The large assay balance, repre¬ 
sented by fig. 11, is admirably 
suited for weighing this apparatus. 
100 grains of the ore are intro¬ 


duced into the flask A, which is then 
filled with water to about one-third; the apparatus is 
closed by the wax stopper, and brought into equilibrium 
on the balance by a counterpoise. The decomposition of the 
carbonate under examination is now induced by sucking out 
a small quantity of air with the mouth from the tube d. 
The air is thus drawn not only from B , but also from A , both 
flasks being connected by the tube c ; bubbles of air are 
therefore seen passing from A through the sulphuric acid ; 
and in order to restore the equilibrium of pressure, a small 
quantity of sulphuric acid is forced from flask B into flasks, 
where coming in contact with the carbonate under examina¬ 


tion, it decomposes it ; and the carbonic acid evolved with 
effervescence in A can only escape by the tube c into the 
flask L>, whence it must pass through the remainder of the 
sulphuric acid and the tube d into the air. This sulphuric 
acid condenses with great energy all the aqueous vapour, and 
retains everything that the current of gas might possibly 
carry with it. When the operation of removing a small 
quantity of air by the mouth, and the consequent addition 
of corresponding quantities of sulphuric acid to the contents 
of flask A , have been repeated until no more effervescence 
ensues, the decomposition is complete. 



















BLOWPIPE REACTIONS OF IRON ORES. 


293 


There is still, however, a portion of carbonic acid remain¬ 
ing in the apparatus which was previously filled with air, 
and some still clings to the solution in the flask A, which by 
this time lias become cold. Both must be removed before 
the apparatus is re-weighed. For this purpose, by suction, 
as in the commencement, at cZ, so much sulphuric acid is 
caused to pass over at once as will give rise to a considerable 
elevation of temperature in A. by which means the carbonic 
acid in solution is evolved, and with it that portion still 
clinging to the other parts of the apparatus. By removing 
the wax stopper b , the mouth of a is opened, and air may 
then be drawn through the apparatus from d until all the 
carbonic acid is expelled. Here, too, all the moisture which 
is removed by the current of air from A will remain in the 
sulphuric acid in B. When the whole apparatus has cooled 
it is placed upon the scale, and the amount of carbonic acid 
is ascertained by the weights which must be added to re¬ 
establish the equilibrium. 

Determination of Water. —Weigh 100 grains of the ore, 
and ignite for a quarter of an hour in a lightly covered pla¬ 
tinum crucible. When cold, weigh the ignited ore ; the loss 
is carbonic acid and water. Deduct the amount of carbonic 
acid previously obtained from the total loss, and the re¬ 
mainder represents the quantity of water. 

BLOWFIPE REACTIONS OF IRON ORES. 

Iron Ores. — Sulphuret of Iron (Magnetic Pyrites ).— 
Alone , undergoes no change before the blowpipe. In the 
open tube , gives sulphurous acid. On charcoal , becomes 
red in the outer flame, and is changed, by roasting, into an 
oxide of iron. 

Common Pyrites.—Alone , in the matrass, exhales an 
odour of sulphuretted hydrogen, whilst sulphur is eliminated. 
On charcoal it behaves like magnetic pyrites. 

Mispickel , Arsenical Pyrites.—Alone , gives first a red 
sublimate, which is sulphuret of arsenic, then a black; and 
lastly, in a strong fire, metallic arsenic sublimes. 

On charcoal , mispickel gives a thick smoke of arsenic, 


294 


BLOWPIPE REACTIONS OF IRON ORES. 


then fuses, exhaling the odour of that metal. If the mis- 
pickel contain cobalt, it can be detected after well roasting 
the ore, and fusing the residue with borax or microcosmic 
salt; after cooling, the glass takes the characteristic colour 
of cobalt. 

Magnetic Oxide of Iron , and Oxide of Iron , behave as 
already described. 

Carbonate of Oxide of Iron , heated in the matrass, gives 
no water. Some species decrepitate strongly. Exposed to 
a gentle heat, it blackens, and gives oxide of iron, very at¬ 
tractable by the magnet. 

Chromate of Iron.—Alone , undergoes no alteration. 
With borax and microcosmic salt, the solution is slow but 
complete. The characteristic colours are alone apparent 
when the bead is hot; but as soon as it cools, the fine 
green of chromium makes its appearance. This reaction is 
most intense when the substance is treated in the reducing 
flame, and appears in all its lustre by the addition of tin. 

Hydrated Oxide of Iron gives water in the matrass, and 
leaves red oxide after fusion with microcosmic salt; it 
gives with tin some traces of copper. 

Oxides of Iron.— Alone , undergo no change in the oxidising 
flame; but in the reducing flame the first two blacken and 
become magnetic. 

With borax they give a dull red glass in the oxidising 
flame, which brightens on cooling, and finally takes a yel¬ 
lowish tint, or even becomes colourless on cooling. If the 
bead contain a very large proportion of oxide, it is opaque 
in the liquid state, and, on cooling, becomes a dull impure 
yellow. In the reducing flame, it becomes bottle-green, 
and, if the reduction be forced to the highest possible extent, 
assumes a lively bluish-green tint, exactly like protosulphate 
of iron. Tin very much accelerates the reduction of the 
higher oxides to the state of protoxide. 

With Microcosmic salt they behave as with borax, but the 
green colour disappears more completely, and may be en¬ 
tirely got rid of by the application of tin. 

Soda does not dissolve the oxides of iron,, but causes them 
to be absorbed by the charcoal, in which they are easily 



BLOWPIPE REACTIONS OF IRON ORES. 


295 


reduced, and may be obtained as a grey, magnetic, metallic 
powder. 

The following method for distinguishing protoxide of 
iron from the sesquioxide, is given by Chapman in the 
4 Chemical Gazette:’— 

A very minute quantity of oxide of copper is to be dis¬ 
solved in a bead of borax on the platinum wire until the 
glass acquires a slight coloration; the substance under ex¬ 
amination now being added to it, the whole is subjected, for 
an instant only, to the reducing flame, when, if protoxide of 
iron was present in the assay matter, the oxide of copper 
will be reduced to suboxide, forming small red spots or 
streaks which become visible as the glass cools. The oxide 
of iron is converted into sesquioxide at the expense of the 
oxygen of the copper. 

In the above experiment, if the glass were exposed for 
too long a time, the oxide of copper might be reduced, even 
if the substance under examination contained only sesqui¬ 
oxide of iron, as this would be converted by the flame into 
protoxide, and thus act, as before stated, on the oxide of 
copper ; and if, furthermore, this latter substance were con¬ 
tained in too large a quantity in the borax glass, it might 
become reduced by the sole action of the flame, and thus 
give rise to an error. To obviate, therefore, all doubt as to 
the presence or absence of protoxide of iron, the same au¬ 
thority proposes that the operation should be conducted in 
a different manner, which gives certain results. 

The borax bead must be coloured by a sufficient quantity 
of oxide of copper to render it of a fine blue colour, but 
transparent when cold. To this the substance under exami¬ 
nation in powder must be added, and then exposed for a 
moment, or until the iron compound .begins to dissolve in 
the oxidating flame. 

If sesquioxide of iron alone be present, the glass will re¬ 
main transparent, and of a green or bluish-green colour ; but 
if, on the contrary, the iron is in the state of protoxide, the 
glass, on cooling, will be marked with opaque red patches, 
due to the reduction of oxide of copper into suboxide, as 


296 


BLOWPIPE REACTIONS OF IRON ORES. 


before explained. Care must be taken not to continue the 
blast too long, otherwise the suboxide of copper might again 
be oxidised, and the whole of the protoxide of iron be con¬ 
verted into sesquioxide. After one or two trials, however, 
no error can possibly arise. The reactions are not prevented 
by the presence of silicic or other acids. 


297 


CHAPTEE X. 

TIIE ASSAY OF COPPER. 

In the assay of copper by the dry way, all minerals and 
substances containing that metal may be divided into three 
classes. 


Class I. Comprises Sulphuretted Ores or Products , with 
or without Selenium , Antimony , or Arsenic. 


Copper glance, Cu 2 S, containing 79’7 p. c. 

Chalcopyrite, Cu 2 S,Fe 2 S 3 , „ 34*4 „ 

Erubesoite, 3Cu 2 S,Fe 2 S 3 , „ 55'7 „ 

Bournonite, 3Cu 2 S,SbS 3 + 2(3PbS,SbS 3 ) „ 12’7 „ 

Fahlerz, 4(Cu 2 S,FeS,ZnS,AgS,HgS).(SbS 3 ,AsS 3 ,Bi 2 S 3 ) 


Covelline, CuS, 

Wolfsbergite, Cu 2 S,SbS 3 , 
Domeykite Cu 6 As, 

Copper regulus, Copper speiss, &c. 



30—48 



66-7 



24*9 


>> 

71*6 

>> 


of copper. 


n 


Class II. Oxidised Ores and Products. 


Red copper, Cu 2 0, 

containing 88 - 7 per cent, of copper. 

Malachite, 2Cu0,C0 2 + H0, 

>> 

57-3 

>> 

5 ) 

Auzurite, 2Cu0,C0 2 + Cu0.H0 

>? 

55*1 

>> 

)) 

Cyanosite, CuO,S0 3 -j- 5HO, 


25-3 


)> 

Phosphate of copper, 

>> 

30—56 


)7 

Arseniate of copper, 

ft 

25—50 


>> 


Chromate, Vanadate, and Silicate of Copper; Slags, &c. 


Class III. Copper and its Alloys. 


The different methods of assaying copper are more nu¬ 
merous than those for any other metal. They are, in some 
cases, very similar to each other, and in others based upon 
very different principles. 



298 


CLASSIFICATION OF TIIE COFFER ASSAYS. 


These methods may be classified in the following 
manner:— 

A. Assay in the Dry Way. 

a. For rich Ores and Products of Class I. 

1. English Copper Assay. 

2. German Copper Assay. 

b. For poor Ores and Products of Class 1. 

1. Fusion of the ore, &c., to a crude regulus, and further treatment of 

the same according to a 2. 

2. Fusion of the roasted ore with reagents to collect the copper (lead, 

antimony, or arsenic), and refining the crude copper. 

c. For Ores and Products of Class II. 

1. Reducing and solvent fusion , with or without collecting agents 

(antimony, arsenic, lead), for the copper, after the ore has been 
roasted, if necessary (in the case of cyanosite and arseniate of 
copper) with coal dust, graphite, or carbonate of ammonia. 

2. Concentration smelting with pyrites to a regulus, which is then 

roasted and smelted to crude copper with or without collecting 
reagents for the copper. 

cl. Copper and its Alloys. (Class III.) 

Refining with lead on the cupel, or with borax on the refining dish, 
with or without the addition of lead, antimony, or arsenic. 

B. Assay in the Wet Way. 

I. For Substances rich in Copper . 

a. KerVs modified Swedish Assay. 

b. Assay of copper by metallic zinc. 

c. Colorimetric Copper Assays. 

1. Heine’s method. 

2. Jacquelin’s and von Hubert’s method. 

3. Muller’s assay with complementary colorimeter. 

d. Volumetric Copper Assays. 

1. Pelouze’s method. 

2. Dr. Penny’s method. 

3. Kunsel’s method. 

4. Parkes’ and Mohr’s methods. 

5. Schwarz’s method. 

6. Brown’s method. 

7. Fluk’s method. 

8. Fleitmann’s method. 


ENGLISH COPPER ASSAY. 


299 


e. Other Copper Assays. 

1. By Levol. 

2. By Robert and Byer. 

3. By Rivot. 

4. By Wolcott Gibbs. 

/. Copper Assays by the blowpipe. 


A. ASSAY IN THE DRY WAY. 
a. For rich Ores ancl Products of Class I. 

I. ENGLISH CO ITER ASSAY. 

M. L. Moissenet has given in the 4 Annales des Mines’ * a 
very complete description of the English method of assaying 
copper by the dry way. The following is from a translation 
by Mr. W. W. Procter. 

Each of the large Swansea copper works keeps an assayer 
at Cornwall, whose duty it is to determine the richness in 
copper of all the lots of minerals of the county sold every 
Thursday at the Ticketing, and of all the samples of foreign 
minerals and copper products which may be useful to the 
smelter. 

It may be asserted that in the course of a year there are 
but a few copper mines being worked on the surface of 
the globe of which some sample has not been addressed to 
the master assayers of Cornwall, and in the same interval 
each laboratory has made not less than 8,000 to 10,000 
assays. 

In consequence of the great number and variety of the 
matters to be treated, and the necessity of having a prompt 
answer, we see the necessity of a simple and expeditious 
method. It is natural, then, that the dry way should be 
preferred to the wet way ; besides, other considerations 
support this choice. 

The copper being obtained in the state of prill or metallic 
button, the impurities (generally tin, antimony, &c.) are 
thus made evident, and the hammer soon proves the quality 


* Yol. xiii. p. 183. 



300 


ENGLISH COITER ASSAY. 


of the metal which we ought to expect to obtain by metal¬ 
lurgy treatment. As for the accuracy of the method, as far 
as regards the whole of the metal obtained, I shall revert 
to this later on. I would, however, observe that, within 
certain limits, the method would not be less practical on 
account of being inexact; for we must not forget that it has 
chiefly for its object to teach the smelter the value of the 
mineral even more than its true richness. 

.For example, if we get too low an assay from a sample 
of 2 or 3 -per cent., we should only from this assent to the 
opinion of the metallurgist, whose interest it is not to work 
upon very poor minerals. The same remark will apply to 
the case of minerals very antimonial, &c. Besides, in the 
description of the method we shall discover the principal 
phases of the Welsh process ; so that it is more just to con¬ 
sider the Cornish assay as a metallurgy on a small scale than 
as a scientific laboratory method. From thence result also 
the necessity of long practice and the almost uselessness of 
theoretical knowledge for those who purpose employing this 
method alone. 

Sir Henry De la Beche (‘Beport on the Geology of Corn¬ 
wall,’ &c. p. 595), in giving a sketch of the method, declares 
it to be rather rough and uncertain, and fails not to add at 
the conclusion a translation of a passage relative to the 
assay of copper pyrites from M. Berthier’s treatise on assays 
by the dry way. 

These drawbacks upon the scientific value of the English 
method cannot injure the power of facts; they constitute 
but another reason which we may have for giving an account 
of the manner in which the first basis of the valuation of the 
greater part of the copper minerals has been fixed since so 
long a period. 

Division Adopted .—The rather complex operations 
through which we have to pass will be better apprehended, 
I think, by explaining in succession— 

1. The order of the operations, the nature and influence 
of the fluxes employed, the kind of products obtained 
(reactions). 

2. The manipulations to which each operation gives rise, 


ENGLISH COPPER ASSAY. 


301 


the furnaces and apparatus used, the characters of the prin¬ 
cipal products during the chief phases and at the end of 
each (manipulations). 

I shall add to these— 

3. Some information upon the influence of the principal 
foreign metals (tin, antimony, zinc, lead), and upon the 
treatment of some special coppery matters. 

4. Summary considerations on the result of the English 
method compared with those of the analysis by the wet 
way. 

Sect. I.—Reactions. 

At the very outset we distinguish two kinds of assays. 

1. The roasted sample. 

2. The raAV sample. 

The first only applies to cupreous pyrites or to samples 
essentially formed of it—-that is to say, which contain sul¬ 
phur in excess : the process begins by a roasting. 

In the raw assay we dispense with the roasting; we 
have recourse to the addition of reagents, either oxidising: 
or sulphurising, according to the minerals ; we endeavour to 
place them by these mixtures in the condition of a properly 
roasted pyritic mineral. 

From this point, at least in general, the operations become 
identical. They consist in— 

1. Fusion for regulus (regulus). 

2. Calcining the regulus (calcining). 

3. Fusion for coarse copper (coarse copper). 

4. One or two fusions with fluxes (washings). 

5. Trial by striking with a hammer, last refining (test¬ 
ing, refining). 

C. Treatment of slags for prill. 

All the slags except those of the fusion for regulus have 
been preserved. The fusion No. 6 gives a small sup¬ 
plementary button of copper, which again undergoes, if 
necessary, one or two washings. 

As I have said, the roasting is used only for pyrites. I 
shall return later on to the duration and the circumstances 
of this operation. Its evident aim is to drive off the excess 



302 


ENGLISH COPPER ASSAY. 


of sulphur, so as to cause the whole of the copper, with a 
part only of the iron which abounds in the pyrites, to pass 
into the state of sulphide at the time of the fusion for 
regulus. 

I. llcgulus. 

1. Py rites .—The fusion for regulus of a properly roasted 
pyrites is made by mixing with it equal volumes of the 
three fluxes, borax, fluor-spar in powder, lime slaked in 
powder, of each one ladle, and covering the mixture with 
a layer of moist common salt. The matters composing the 
gangue of the roasted mineral consist principally of quartz, 
silica, and in general of more alumina and magnesia than 
lime ; oxide of iron, resulting from the roasting of the pyrites 
is also present. 

The borax only serves to give fusibility, the fluor-spar 
contributes’to the same end by forming a fluosilicate. I do 
not think that it otherwise plays an important part in the 
decomposition—that is to say, that there may be a produc¬ 
tion of fluoride of silicon and calcium ; for this last base is 
added here in considerable proportion, so as to form im¬ 
mediately a silicate which may combine with the fluoride of 
calcium. 

The peroxide of iron being reduced to pass into the 
slag, and the different metallic oxides to pass into the 
regulus, yield oxygen, which reacts on the remaining 
sulphur. The disengagement of sulphurous acid which 
results from this, joined to the water contained in the 
fluxes, justifies, to a certain extent, the use of a bed of 
common salt, designed to prevent the boiling over. Besides 
this, the common salt being without action on the metallic 
sulphides, does not here produce those important effects 
which I shall point out in the later fusions. 

If the pyrites appear insufficiently roasted, we must add 
a little nitre, the oxidating action of which again gives 
off sulphur; the opposite case, that of a roasting too 
much prolonged, is rare ; we remedy it by the addition of 
sulphur and tartar, as I shall indicate for other sorts of 
minerals. 

2. Very poor Pyrites .—In a very poor pyrites—that of 



ENGLISH COPPER ASSAY. 


303 


Bear Haven, in Ireland, for example—the proportion of 
sulphur does not require us to have recourse to the roasting ; 
we employ the three fluxes and one ladle of nitre. 

3. Variegated Copper Ore. —Peacock ore contains less 
sulphur in proportion to the copper than pyrites; we also 
fuse with a little nitre. 

4. Sulphide of Copper. —The sulphur is here insufficient. 
We add together sulphur \ to 1 ladle, according to the 
valuation; tartar ^ to ^ ladle—that is to say, half the volume 
of the sulphur. The tartar is a powerful reducing agent, 
and is supposed in small quantities to favour the action 
of the sulphur by preventing its disengagement as sulphur¬ 
ous acid by the oxidating matters in the mineral; but if 
used in excess, it acts as a desulphuriser, as well by its 
carbon as by its. alkali. 

5. Carbonated Minerals. —The addition of sulphur and 
carbon is evidently still more necessary here. 

6. Native Mixture : f sulphide copper, J pyrites.—We 
add, in this case, nitre for the pyrites, and sulphur and 
tartar for the sulphide of copper; although these reagents 
appear sure to neutralise each other, it is possible that their 
simultaneous employment may be logical. The nitre pro¬ 
bably decomposes the pyrites, which would, without it, fuse 
and give a very ferrous regulus, whilst the free sulphur 
would be of little use, on account of the sulphide of copper. 
Be this as it may, this is the plan adopted. 

During the progress of the fusion for regulus we have still 
to introduce other matters, some accidentally, and others in 
all cases. 

If a blue flame persists in escaping from the crucible, an 
index of the formation of sulphurous acid, we project into it 
sulphur 1 ladle, tartar h a ladle. When the fusion appears 
almost finished, in order to render the bath more liquid, and 
to facilitate the collection of the button, we throw in a 
little dried salt and a flux composed beforehand of lime, a 
little fluor-spar, and a very little borax—that is to say, of 
the elements in different proportions of the mixture intro¬ 
duced originally. 

The regulus obtained is composed principally of copper, 



304 


ENGLISH COPPER ASSAY. 


iron, and sulphur. I shall return to the aspect and the 
richness which it ought to have according to the minerals 
treated. 

II. Calcining . 

The calcination of the regulus is one of the most im¬ 
portant operations; it ought to be quite complete. 

III. Coarse Copper. 

To the calcined regulus is added—nitre \ ladle, borax ^ 
ladle, charcoal -g ladle, dry salt 1 ladle. These quantities 
remain the same, whatever mineral may be assayed—tartar 
2 ladles. Case of medium richness. Covering of moist salt, 
2 ladles. 

The nitre is designed to burn the sulphur which may 
have escaped the calcining, and to ensure the passage of the 
easily oxidisable metals, especially of iron, into the slag in 
the state of oxides. It is besides in too small proportion to 
act upon the copper, especially in presence of reducers 
whose effect is certainly later than the deflagration of the 
nitre. 

The borax plays simply the part of a flux. 

The dry salt has for its object to give fluidity to the slag. 
Unfortunately, if the addition of the salt attains this object, it 
also determines from this operation a sensible loss of copper 
by carrying it away with the saline vapours. I shall insist 
upon this point in describing the washing. 

The charcoal and the tartar are especially the important 
reagents in the fusion. The tartar, at the same time that it is 
one of the most energetic reducers, is also a flux and a desul- 
phuriser. Its use is, then, perfectly justified here, only the 
proportion of tartar added ought to be regulated according 
to the quantity of copper, which the weight and aspect of 
the regulus permit the experienced assayer to estimate suf¬ 
ficiently close; an excess of tartar would reduce the foreign 
metals, and produce in consequence a very impure coarse 
copper. 

When the fusion appears complete, we throw in a pinch 


ENGLISH C0ITEE ASSAY. 


306 


of white flux,* which gives fluidity to the slag, and deter¬ 
mines by its partial decomposition, from which a disengage¬ 
ment of carbonic oxide results, a stirring up of the materials. 
These two effects facilitate the collection of the metallic 
button. The carbonate of potash begins also without 
doubt from this operation to refine the metal a little by at¬ 
tacking the iron, zinc, and tin already reduced. M. Berthier 
( 4 Essai par la Voie Seche,’ vol. i. p. 393) points out this 
reaction :— 6 A part of the carbonic acid which it contains 
being decomposed and changed into carbonic oxide, a com¬ 
pound is formed consisting of alkali, carbonic acid, and 
metallic oxide, &c.’ 

Lead, copper, and antimony are not attacked. 

IV. Washings. 

In the operation of washing we put into the crucible at 
the same time as the coarse copper the following fluxes : — 
White flux, 1 ladle ; dry salt, 2 ladles. 

It is evident that the white flux is here employed as an 
oxidiser of the foreign metals, and with a view of the applica¬ 
tion of the above-mentioned reaction. 

As for the salt, it is both useful and injurious. If it were 
only used with the view of augmenting the fluid mass so as 
to preserve the metal from contact of air, &c., it would be 
advantageously replaced by an excess of white flux ; but it 
can form with the arsenic and antimony which the copper 
has retained in the form of arseniuret and antimoniuret, 
volatile chlorides. Common salt is, then, to be regarded as 
one of the principal agents of purification put in operation 
by the English method. On the other hand, the loss of 
copper which arises from the carrying off of this metal by 
the vapours of common salt cannot be doubted. M. Ber¬ 
thier has found that by heating equal weights of copper and 
salt until the complete volatilisation of this last, 3 per cent, 
of the metal is carried off. 

* This white flux is prepared in the laboratory by mixing in a mortar, 
tartar 3 volumes, nitre 2 volumes, salt a little, then determining the combus¬ 
tion bv the introduction of a red-hot iron rod, which is turned round until 
the matter ceases to deflagrate. 


X 


306 


ENGLISH COPPER ASSAY. 


In the event of the coarse copper appearing too impure, 
we take care to add a little nitre. According to the appear¬ 
ance of the button we recommend the washing or not. 

V. Testing , Refining . 

The button of metal is flattened on an anvil. We thus 
recognise tin by the hardness and antimony by the brittle¬ 
ness of the alloy. The button is then put alone in the cru¬ 
cible. When it presents a proper appearance—that is, 
when the edges assume a bright colour, the centre, which 
the assayer calls the eye, being dark—we hasten to put into 
the crucible the fluxes, which are the same as for washing, 
only taken in rather smaller quantity. 

In general, when we have operated well the button ob¬ 
tained is of a fine colour, and is regarded as pure ; if we have 
passed the eye, it is covered with a layer of red oxide; if, 
on the contrary, we have put in the fluxes too soon, the 
button is dull. 

It is easy to give an account of the reactions which take 
place during the refining, and which differ a little from those 
of the washing. 

In heating the button alone in the air in the crucible, it is 
intended to submit it to an oxidation, which ought to act 
sufficiently on all the foreign metals more oxidisable than 
copper without acting too much on this last. The proper 
point is indicated by the appearance of the eye : the projec¬ 
tion of the fluxes puts an end to the atmospheric oxidation, 
and determines the scorification of the oxides which expel 
part of the carbonic acid of the carbonate of potash, for 
which they substitute themselves, and give rise to triple 
compounds of metallic oxides, alkali, and carbonic acid. 

The oxides of lead, tin, iron, and zinc comport themselves 
thus. When we have passed the eye, there has been a con¬ 
siderable formation of oxide, which leaves the button 
reddened, as I have indicated. At the same time the slag 
is strongly coloured red or green. If, on the contrary, the 
fluxes have been thrown in in too great haste, the oxidation 
has been insufficient, and then the refining just falls back 


ENGLISH COPPER ASSAY. 


307 


upon the preceding operation of washing—an operation less 
efficacious and even without result in the case of lead and 
antimony. 

As for the physical phenomenon of the eye, perhaps it 
corresponds to the very short instant when the oxides, less 
dense than the copper, are concentrated at the top of the 
button, and there make a dark spot before attaining a tem¬ 
perature sufficiently elevated to acquire the brightness of 
the metal itself. 

I shall add that the minerals of Cornwall, generally more 
impure than foreign minerals, require a notably longer time 
for the appearance of the eye. 

Extra Accidental Washing .—More often the refining 
gives a definite product, put aside to be weighed with the 
prill extracted from the slag; let the button be clear, burnt, 
or dull. Even if the metal appeared too impure we would 
not recommence the refining, but would have recourse to an 
extra washing by putting at once into the usual crucible 
besides the button and the usual fluxes, the slag from the 
refining. 

YI. Slags for Prill. 

All the slag from the fusion for coarse copper inclusively 
having been preserved, we fuse them altogether with— 

Tartar ... 1 ladle) Simple reducing 

Charcoal . . . traces i mixture. 

We obtain a small globule variable with the circumstances 
of the different operations which have allowed more or less 
copper to pass into the slag. If the prill is not very small, 
and its appearance indicates a metal not sufficiently pure, 
we submit it to one or two washings, as above. 


Sect. II.—Manipulations. 

The sample, which has been taken with the utmost care, 
arrives at the laboratory rather coarsely powdered, still wet, 
and wrapped in strong packing paper : the paper is opened 
and placed near a furnace on the cast-iron plate which 
covers it; the drying is rapidly done there. 



308 


ENGLISH COPPER ASSAY. 


The first question is to discover the kind or kinds of 
minerals, so as to employ the warm or raw sample. 

For this purpose we throw one or two large pinches of 
the mineral into a flat-bottomed copper dish, and we wash 
it very easily by putting in water several times and giving 
a rotatory motion to the matters, at the same time that we 
incline the dish so as to cause the muddy parts to run from 
the gangue. The small metallic fragment remains distinctly 
visible, and we can often discern by simple inspection the 
presence of foreign metals. 

We weigh 400 grains of the dried mineral, a quantity 
upon which the assay is made. 

The crucibles used in Cornwall are of three sizes :— 

1. Large. 

2. Large second. 

3. Small second. 

The small seconds have externally the internal dimensions 
of the large, into which they fit as into a nest; the first and 
third are sold the one in the other, and called nested. They 
are the most used. 

The large serve for the roasting and the fusion for regu- 
lus, the small second for calcining the regulus and all the 
fusions which follow. 

The large seconds are only employed in place of the for¬ 
mer when we have to treat a very large regulus. 

The crucibles are of a kind rather wrinkled, and as if fused 
superficially, they present the appearance of coarse stone¬ 
ware pottery. Their form, moderately wide, permits us to 
make use of them successively for the roasting and the 
fusion for regulus, and gives them sufficiently great stability 
in the fire of a wind furnace. They are besides very re¬ 
sisting. They are made at Truro and Redruth.* 

The wind furnace has for its principal dimensions— 


Length from front to flue 
Breadth 

Depth to the bars . 


Opening of the flue 


f length 
\ height 


Inches 

10 

8 

14 

8 

2 


* Mr. Juleff, of Redruth, is considered to make the best crucibles. Each 
laboratory uses 1,500 dozens annually. A lid is never used for the crucible. 






ENGLISH COPPER ASSAY. 


309 


A sufficiently large space is reserved underneath the fire, 
where the ashes accumulate without inconvenience, but 
opening only by a framework contracted so as not to allow 
too free an access of cold air. 

The furnace serves either for roastings or for fusions; in 
the latter case we cover it with two mounted bricks, very 
easy to manage, and allowing to only half open it when we 
wish to inspect the contents of the crucibles. We can con¬ 
duct ten roastings at once ; the crucibles are marked by a 
brush with colcotliar mixed with water. The furnace having 
been recharged with coke, we put the crucibles on the top, 
and after a few minutes, the substances beginning to get 
warm, we stir them by means of iron rods. Each crucible 
receives a rod which we leave standing there (leaning 
against the chimney) during the whole period of the roast¬ 
ing, so as to avoid the loss which would take place if we 
withdrew the rod. From time to time we renew the sur¬ 
faces by lightly taking hold of the rod with the left hand 
by the upper end, whilst the right forefinger and thumb 
make it turn at once upon itself and round the crucible. 

The duration of the warming varies essentially with the 
nature and the richness of the mineral; it is never less than 
six or seven minutes, and may reach half an hour. When 
from the sandy appearance of the matters we consider the 
operation finished, we withdraw the crucible, raise the iron 
rod with care, and expose the crucible to the air, allowing 
its contents to cool slowly. The roasting has succeeded 
when the surface has the brown red colour of oxide of iron 
and the bottom only is black. In this case we proceed to 
the fusion for regulus by simply adding the three fluxes 
(borax, fluor-spar, and lime); if the bottom of the crucible 
appeared too black, we ought to complete the oxidising 
action by the addition of a little nitre. 

Fusion for Regulus. 

The different substances above indicated are taken from 
the box with a slightly concave ladle of 1§ diameter, then 
mixed in the crucible with a stirring-knife. We ought to 


310 


ENGLISH COPPER ASSAY. 


allow the heat of the wind furnace to fall and to recharge, 
so as to have a gentle fire at the commencement of the 
fusion for regulus. The crucibles are placed upon the coke, 
and supported against the walls of the furnace, which we 
then close with the two bricks. After about a quarter of 
an hour, we open the front brick so as to observe the pro¬ 
gress of the operation; it is at this stage that we throw in 
the sulphur and tartar into those crucibles from which a 
blue flame is disengaged. Some minutes later—that is to 

D O 

say, nearly seventeen minutes from the commencement, we 
add the salt and the flux destined to collect the regulus ; 
then (twenty minutes from the beginning) we run into a 
metal mould, not greased. 

We make, in general, several fusions at once—four, for 
example ; we have in consequence two moulds into which 
we pour the contents of the crucibles in an adopted order, 
so as to avoid all confusion. The matters, very rapidly 
solidified, are detached simply by a blow, and fall in order 
on a metal plate fixed in front of the laboratory window. 
We immediately seize them with the copper tongs, put 
them into a basin of the same metal, and immerse them for 
a moment in cold water, where it is important not to leave 
them too long. This immersion allows us then to separate 
very easily the slag from the button of regulus, itself very 
brittle. For this purpose the fluxions are put on the metal 
plate, and by means of a hammer we strike with care all 
round the slag, which breaks off pretty cleanly. We hasten 
to detach from the surface of the regulus the slag which 
may remain adherent, using a small hand chisel, without 
the hammer. The slags are broken, and if we find any 
prills of regulus they are added to the principal button. 
Sometimes in these breakings, and especially in those analo¬ 
gous for the last fluxings, we surround the substances by an 
iron ring, placed on the metal plate, so as to avoid loss of 
splinters. In a general way, the slags of the fusion for 
regulus are rejected. We shall see further on how it may 
become necessary to flux them again when the mineral con¬ 
tains blende. 

The aspect of the regulus is characteristic, and it is easy 



EXGLISII COPPER ASSAY. 


311 


to arrive at a pretty close estimation of its richness, and 
consequently of the degree of success of the operation, by 
simple inspection of the regulus. 

No. 1. A regulus very poor (coarse), that is to say, too 
much charged with iron, is bronzed and dull; the operation 
following would not be able to carry off the excess of iron, 
at least without a corresponding loss of copper. A like 
regulus evidently results from an imperfect warming, or 
from an excess of sulphur, or from an insufficiency of nitre, 
as the case may be. 

It contains less than 40 per cent, of copper. There is 
nothing for it but to reject it. 

No. 2. A regulus of good appearance is in general bronzed 
but rather shining; it appears liner. Its richness varies from 
40 to 60 per cent. 

No. 3. From oxides, carbonates, and from some minerals 
charged with impurities (SnSb) we desire to obtain a fine 
bluish button of a greater richness—65 to 75 per cent. We 
perceive, indeed, that for oxides and carbonates, to which 
we have only to add sulphur, and which also by their na¬ 
ture do not, like pyrites, contain combined iron, it is easy to 
obtain a richer regulus without fearing any loss of copper. 
As for the stanniferous and antimonial minerals, I shall 
return to them further on. 

No. 4. In every case a regulus, the richness of which rises 
to 80 per cent., and of a very shining grey blue appearance, 
ought to be rejected, its richness indicating the loss of a 
certain quantity of copper left in the slag. 

Here is, in the preceding order, the result of the analyses 
of four buttons whose description agrees with that which I 
have just given, excepting, perhaps, No. 2, whose fracture is 
rather reddish :— 


No. 


Copper 

Iron 

Balance; 
sulphur 
&i traces 
of foreign 
metals 

1 . 

Coarse, to be rejected 

36-00 

32-90 

3M0 

2. 

Good in general (rather too fine) 

60-00 

14-70 

25-30 

3. 

Good for a carbonate, &c. 

65-60 

10-50 

13-90 

4. 

Too fine, to be rejected . 

80-16 

2-10 

17-74 
















312 


ENGLISH COPPER ASSAY. 


If we compare these products with those obtained in the 
metallurgy of copper by the Welsh method, we find (Le 
Play, c Annales des Mines ’):— 


Matts of the operations. 
II. V. IV. VIII. 


V. 


Coarse matt (fusion of poor mine- 
II. 1 rals, raw or calcined) 

8Cu a S+Fe 2 S3+4(Fe. dif. met)S 
Blue matt (fusion of the calcined 
coarse matt with minerals of 
mean richness) 

0-8Cu+3Cu a S+2(Fe. d.m.)S 
Reddish variety, matte mince 

| l-3Cu+3Cu a S+2(Fe. d.m.)S 

f White matt (fusion of the calcined 
coarse metal with rich minerals, 
carbonates, and oxides) 

IV. ■{ Metal—very pure type . 

very blue variety 
mean . . ' . 

8Cu a S + FeS 

Matt (roasting of extra white matt ’ 

viii. -! vii.) 

. 0-2Cu+Cu a S 


Copper 

Iron 

Different 

metals 

Sulphur 

Total of 

Diff. M. & S. 

34-6 

341 

1-5 

1 298 

31-3 

57-2 

18-5 

10 

233 

24-3 

61-6 

15-8 

0-6 

220 

22-G 

77*4 

0-7 

0-9 

21 0 

219 

64-8 

9-0 

3-6 

22-6 

26-2 

73-2 

6-3 

— 

20*5 

“ 1 

81-1 

1 

0-2 

— 

18*5 

— 


These numbers show the evident analogy, the identity 
almost, of the products of the laboratory and those of the 
works ; we may sum up by saying that the regulus ought to 
be richer than coarse metal, and in the case of ordinary 
minerals to approach if not to attain (as in the case of 
sample No. 2) to the composition of blue metal. 

For carbonated and oxidated minerals we arrive directly 
at the very bluish variety of white metal. 

Finally, in no case must we arrive at a button as rich as 
regulus matt. 


Calcining the Matt. 


The matt is pounded fine in a bronze mortar; we avoid 
loss of fragments by means of a perforated cover and a 
cloth which surrounds the pestle. To facilitate the pulveri¬ 
sation, and avoid the sulphuret greasing, we add in the 
mortar a small piece of coke. The pounded matt is 
carefully turned upon a sheet of paper, the mortar wiped 












































ENGLISH COPPER ASSAY. 


313 


out with a liare’s foot, and the substance put into a small 
second or large second crucible. The calcining is conducted 
as the warming of a mineral; it generally lasts longer, for 
the expulsion of the sulphur is to be as complete as possible. 
It demands the most minute care to regulate the fire so as 
to avoid all agglomeration, and to stir almost continually. 
When the matter adheres to the rod, we withdraw the cru¬ 
cible for a moment; this inconvenience is chiefly produced, 
if we have not detached the slags sufficiently from the 
matt; the calcining is then much longer, the flames remain 
blue a long time, and the fumes which are disengaged have 
an odour which is not purely that of sulphurous acid. 
When the fumes and the odour cease, and the matter has 
taken a sandy appearance, we raise the heat; then withdraw 
it, and allow to cool slowly in the air as for warming. 

The mean duration of calcining is half an hour. 

Coarse Copper . 

The fluxes above indicated are taken from the box No. 1, 
except the dry salt, which forms part of a second box called 
the refining flux. The ladle for this box No. 2 is a little 
larger than for the first; it has a diameter of -044 m. At 
the beginning of the operation the furnace is well filled and 
lighted ; the same lire ought to suffice for all the following 
fusions, which it is very important to conduct with great 
rapidity. After a moment, and if there is any frothing, we 
throw in some dry salt, which calms the ebullition. At the 
end of ten minutes, the fusion appearing complete, we throw 
in a pinch of white flux. A little after we withdraw suc¬ 
cessively each of the crucibles, pouring them carefully and 
by a single turn into each of the principal cavities of the 
metal mould. These moulds ought, this time only, to be 
greased with a cloth impregnated with suet. The crucibles 
are immediately put back again into the fire. 

We detach the fluxion as previously, seize each one suc¬ 
cessively with the copper tongs, and plunge it for an instant 
into a basin full of water. The rest is effected as for the 
regulus, only the slags are preserved on the metal plate, and 


314 


ENGLISH COPPER ASSAY. 


in the order in which we have detached them. The button 
of copper obtained appears more or less black; I have 
already indicated the influence of the tartar in excess. 

Washings. 

We place the button and the fluxes in a large copper 
shovel, lengthened and narrowed at the end, called a scoop, 
and we pour them into the crucible, which is already at a 
red heat. As the fusion is made in five or six minutes, it 
would be inconvenient to prolong it on account of the loss 
occasioned by the carrying off of copper with the vapours 
of common salt. The tapping is made with care by pouring 
first into one of the large cavities, then as soon as the metal 
has fallen there we finish by pouring in the slag into one of 
the small lateral cavities. This last slag, probably rich in 
copper, is less fluid, and would adhere to the button, which 
would be difficult to cleanse. The two buttons being de- 
tached from the mould, we immerse the small one first, then 
finish as in the preceding operation. 

Testing and Refining. 

The crucible has again been put back into the furnace_ 

after the tapping ; the button tried by the hammer is put into 
the crucible by means of the tongs. At the end of about 
three or four minutes it attains the colour of the vessel, the 
eye manifests itself, and we rapidly throw in the fluxes put 
into the scoop beforehand. 

The tapping is made as for the washing, with the small 
button of slag kept apart. 

In general we arrive at a button regarded as pure, clean 
copper; if not, as I have said, we proceed to an extra wash¬ 
ing by adding exceptionally in the scoop the last slag 
obtained. 

Prill, 

The crucible this time has been left out of the furnace \ 
put into it all the slags, collected for this purpose from 
the metal plate into the scoop, and upon which we have put 


ENGLISH COPPER ASSAY. 


315 


reducing reagents. The fusion lasts a quarter of an hour ; 
pour all at once into the large cavity ; before the cooling, 
by means of a transverse blow, get rid of the upper beds 
which are still liquid, and composed principally of common 
salt. Then operate as above. Collect the prill, which 
again undergoes, if necessary, a washing. 

Sect. III.—Some Minerals and Substances of a Special 
Nature—Influence of Foreign Metals. 

Stanniferous Minerals.— Most often we only perceive the 
presence of tin in a copper mineral when testing with the 
hammer, which reveals the nature of the bronze ; when we 
proceed to the refining of such a stanniferous button it is 
impossible to obtain the characteristic eye; that is to say, 
the surface of the metal becomes quite clear, and we scarcely 
open the furnace when it again becomes obscure. We 
free it from tin by two or three extra washings. If we 
suspect tin from the known produce of the mineral, or the 
inspection of the sample in the basin, we endeavour to obtain 
a fine regulus, which is accomplished in the case of a warm 
sample by prolonging the calcining, and for the raw sample 
by putting in more nitre or less sulphur. It is clear that 
tin can only enter the regulus by virtue of the excess of 
sulphur necessary to the formation of the coppery matt, and 
that by restraining this excess of sulphur we diminish the 
chance of tin entering the button. The fine regulus ought 
to contain 7 0 to 75 per cent, of copper, as for the carbonated 
copper minerals. 

Antimonial Minerals. —Antimony is also detected in the 
testing ; the metal being rendered very brittle. We then 
add one or two grammes (15 to 30 grains) of lead in the 
refining operation. There forms an alloy of lead and anti¬ 
mony heavier than copper, which is poured into the small 
cavity of the mould. When we suspect antimony, we act 
as for tin—that is to say, w T e produce a fine regulus, a most 
careful roasting expelling the antimony ; then we have to 
make two washings, and in the second to add the metallic 
lead. 


ENGLISH COPPER ASSAY. 


31 (> 

We cause, then, three influences to act with a view of 
expelling the antimony :— 

1. Slow oxidation at a low temperature, disengaging 
antimony. 

2. Repeated chloridations, from whence a formation of 
volatile chlorides. 

3. Affinity of the lead and mechanical separation of the 
alloy. 

Zinciferous Minerals. —One of the metals which is most 
troublesome is zinc. We recognise it by the appearance of 
the regulus and by its colour, which is that of blende. 
Once out of ten the regulus collects sufficiently to be able to 
detach it; in this case we pound it, add to it the slags, and 
borax 1 ladle, nitre ^ ladle. We fuse anew, and obtain a 
good regulus, for the nitre has caused the zinc to pass into 
the slag in the state of oxide. 

Most often the zinciferous regulus does not collect, and 
there is nothing for it but to begin anew by making a very 
prolonged warming at least half an hour—for example, 
mineral of South Crenver—this is evidently what we should 
have done at first had we been aware of the presence of the 
zinc. 

Plumeiferous Minerals. —Lead is not injurious, for it does 
not alloy with copper. The warming is also prolonged. 
Lead passes into the regulus, which facilitates the collection 
of the matter. In the last operation the lead easily passes 
into the slag; it also in case of need carries off antimony. 
Thus the copper obtained from lead minerals is most malle¬ 
able. 

Special Cupriferous Products. 

Regulus of Chili.— These are treated as those which we 
obtain by the fusion for regulus. Their richness, which rises 
to nearly 60 per cent., requires us to add much tartar in the 
fusion for coarse copper. 

Slags of Copper.— To obtain regulus we add to the slag 
sulphur, tartar, and nitre; this last maintaining metals other 
than copper in the state of oxide in the slag. 

Old Copper. —For turnings, waste of workshops, &c., 
yielding 97 to 98 per cent, by the assay, and containing, in 




ENGLISH COPPER ASSAY. 


317 


fact, not much foreign matter except a little mixed dust or 
dirt, we take care first to glaze the crucible by fusing in it 
a little borax and nitre ; then we treat the matters by a 
simple washing, the slags of which we work for prill. This 
last is often very considerable. 

Sect. IV.—Summary Considerations—Comparison of the Results 
with the Analysis by the Wet Way. 

After this detailed account of the numerous operations 
which the metal undergoes before attaining the state of 
button and prill, it would, I think, be superfluous to insist 
upon the practical difficulty of the English method. 

Nevertheless, in experienced hands, and in the case of 
daily practice, it is still a rapid method, allowing us to treat 
almost uniformly the different varieties of copper mineral, 
and at the least to remedy during the operation itself the 
impurities which show themselves. 

As to the metallurgic accuracy, here is a small table 
showing comparatively the produce by the dry way (deter¬ 
mined by a Cornish assayer) and that which I have obtained 
by the most precise methods of the wet way. It compre¬ 
hends six samples, whose richness varies within sufficiently 
great limits. 


Nature of the sample 
and produce 

Dry way 

D. 

Wet way 
W. 

Difference 
W - D. 

Regulus of Chili ..... 

561 = 56*250 

58-40 

2-150 

Green carbonate copper of Castile 

9f = 9-750 

11-52 

1-770 

Variegated copper, Huel Damsel . 

10f = 10-500 

11-30 

0800 

Pyrites, West Wheal Seton . 

8§ = 8-375 

8-40 

0-025 

,, United Mines .... 

8 = 8-000 

10-38 

2-380 

,, Devon Great Consols 

4f= 4-625 

5-60 

0975 | 

Mean difference 

s (W-D 

6 

• • 

8-100 

1-350% 


By adding the result given by the last five minerals we 
find 

2D = 41*25, 2(W—D) = 5’95, 5W = 47*20, and 

??_9 44. 

5 


















318 


ENGLISH COPPER ASSAY. 


By taking the ratio 

S(W-D) _ 14 . 42 

V ,D ’ 


we see that we must acid to the richness indicated by the 
Cornish assay about ith of that result, and by taking the 
ratio 


2(W-D) 

sw 


12*60, 


that the loss is -|lh of the copper if we consider a mineral of 
9 or 10 per cent. 

Without wishing to draw a conclusion altogether general 
from so small a number of analyses, I nevertheless think 
they suffice to show that the English method occasions losses 
always sensible and sometimes considerable. I think I may 
assert that upon the whole of the Cornish minerals whose 
mean richness varies from 6 to 7 per cent., the loss by the 
assay is not less than 20 per cent, of the contained copper, 
and that for certain pyrites of 3 to 4 per cent, it attains 30 
and 40 per cent, of the metal. 

The principal causes of these losses are,—(1st) The quan¬ 
tity more or less great of copper left in the slag of the re- 
gulus; (2nd) and especially the carrying away of copper by 
the vapours of common salt in the fusion for coarse copper, 
the washing or washings, the refining and the treatment of 
the slag for prill. 

In consequence, I think they ought to bear principally on 
the oxidated minerals for which we make a rich regulus, and 
still more on the impure minerals, which besides a rich re¬ 
gulus, have undergone several washings. Thus the minerals 
of Algeria, grey copper, assayed some years ago at the 
School of Mines, have given a produce much higher than 
that indicated by the Cornish assayers. 


Conclusions . 

In conclusion, the English method, as applied by the 
buyers and in their laboratories, certainly answers all 
their wants; but indicating results always lower than the 



GERMAN COPPER ASSAY. 


319 


real result, it would appear to be exercised to the detriment 
of the sellers. 

The counter assays which are frequently made on account 
of mining companies and miners tributors can only be a proof 
of the good faith and of the truth of the figures announced 
by the buyer. 

But we must not lose sight of the fact that the industrial 
methods of assay have for their object only to fix a basis of 
buying, and for this purpose it is not necessary that they 
should give a rigorously exact result; it is even logical that 
the loss in the assay should be proportioned to the loss in 
the treatment according to the greater or less impurity of 
the material. 

Thus even if the Cornish companies should come to state 
in their products a richness of 1 or 2 per cent, greater, there 
would not result from this in reality any increase of value 
for their minerals, or, if we like, any advance of the buying 
price. This price is from other reasons far superior to those 
of copper minerals in foreign markets, and especially to that 
which is paid for American minerals at the works at Boston. 


II. GERMAN COPPER ASSAY. 

This assay comprises the following operations :— 

1. The Roasting in the Muffle Furnace . 

From the correctly chosen, properly dried, and prepared 
assay substance, one centner is weighed out in duplicate for 
the assay. The weighed substance is so spread out on a 
roasting dish, that has been previously rubbed with chalk, 
rouge, or powdered manganese, that most of it lies towards 
the margin of the dish, and only a thin layer is found in 
the middle. The assay, which has also been previously 
well mixed with at least two parts by volume of charcoal 
powder, of twenty-five to forty pounds of graphite, is then 
placed in the dull red-hot muffle, and cautiously roasted till 
no more sulphurous or arsenious acid escapes. 

The heat can be raised rapidly or only slowly, and the 


320 


GERMAN corral ASSAY. 


roasting finished in a shorter or longer time, according to the 
composition of the assay sample. 

The presence of lead , arsenic , and especially antimony , 
makes special caution necessary, on account of the easy fusi¬ 
bility of their compounds. Such ores ( e.g . faiderz , bourno- 
nite , &c.), are roasted very gently at first, without the addi¬ 
tion of coal, and afterwards powdered coal is used instead of 
graphite, as the ore thus roasts at a lower temperature. If, 
at the same time, as in many fahlerzen, sulphide of mercury is 
contained in the ore, the latter cakes together at a very low 
temperature, and at a greater heat evolves mercury with such 
rapidity that mechanical loss occurs. Such ores must be 
placed in the muffle while it is yet only moderately warm, in 
order to volatilise the mercury gradually, and be further 
roasted with coal only after the removal of the mercury. 
Coke and graphite work almost exclusively and continuously 
chemically, while charcoal dust has, at the same time, a dis¬ 
integrating mechanical effect, since generally a large part 
of the latter is already burned before the ore has reached a 
temperature at which it can work upon it. 

When the roasting ore has ceased to fume, and no longer 
gives forth any smell of sulphurous acid, it is ground 
in a brass or cast-iron dish, mixed with about twenty-five 
pounds of coal dust, and again roasted at a higher tempera¬ 
ture till the odorous gases produced have disappeared. The 
assay is also sometimes calcined with tallow. If the ore is 
a very difficult one to roast, then, instead of the coal dust, 
a final addition of forty to sixty pounds of carbonate of am¬ 
monia is given, by which the sulphates (even the sulphate 
of lead) are decomposed with the formation of volatile sul¬ 
phate of ammonia. Generally, a second grinding suffices. 
To secure a complete oxidation, it is necessary that the coal 
should be entirely consumed. 

Arsenic can be removed, for the most part, by this roast¬ 
ing ; still some basic arseniates are always formed. Anti¬ 
mony is more difficult to remove, and can only be in some 
measure driven off* by careful roasting and frequent rubbing 
up. It remains behind as antimoniates. A residue of both 
these substances is less injurious than one of sulphur. The 


GERMAN COPPER ASSAY. 


321 


latter occasions in the reduction smelting a formation of 
sulphide of copper, the copper contents of which escape 
determination. 

When no more fumes from the hot assay can be perceived 
by smell or sight, and the assay powder shows a constant, 
uniform, dull colour, and no more grains with metallic lustre 
can be seen while grinding it up, and finally when no more 
particles of coal or graphite can be detected, the roasting is 
finished. 

Only with a completely roasted assay can it be counted 
upon that all, or as nearly all as possible, of the copper has 
been converted into oxide, and this must be accomplished 
if the result of the assay is to be correct. The copper 
which remains in the state of sulphide or sulphate is almost 
wholly lost, as by the later addition of alkaline flux it 
cannot be at all, or only very incompletely, reduced to me¬ 
tallic copper. 

If the assay sample contains sulphates which are not con¬ 
verted into oxides by coal, graphite, and carbonate of ammo¬ 
nia (e.g. gypsum, baryta, &c.), it must be first smelted to a 
matt, which is then treated like a raw ore to be roasted. 
For this purpose one assay centner of ore, one centner of 
borax-glass, one centner of potash or soda glass, and ten 
pounds of colophony are well mixed together, the mixture 
covered over in a small crucible, with about three centner 
of chloride of sodium, the crucible furnished with a cover, 
and the assay heated for half an hour in the muffle, or 
three-quarters of an hour in the wind furnace. The earths 
are thus slagged off, and a cupriferous matt results in the 
shape of a button, which is finefy pulverised and roasted. 


2. The Solvent and Reducing Fusion , 

If the roasted assay, which, besides a small quantity of 
antimoniates and arseniates, may contain the oxides of copper, 
lead, iron, zinc, &c., is subjected to a reduction smelting 
with simultaneous use of solvent agents (borax, glass), then, 
by a suitable and not too high a temperature, the more diffi¬ 
cultly reducible oxides of iron, manganese, zinc, &c,, are in 

Y 


322 


GERMAN COPPER ASSAY. 


great part slagged off, while the oxide of copper is reduced, 
together with a small portion of the above oxides and most 
of the oxide of lead, and yields a button of impure copper 
(black copper), in which also is found almost the whole of 
the antimony and arsenic of the roasted ore. If too much 
solvent flux is used, copper also is slagged, which may be 
known by the red colour of the slag produced. With a lack 
of solvent agents, a great part of the foreign oxides is reduced, 
and a very impure black copper is formed, whose refining 
is attended with greater loss. The charging has been well 
chosen, when with a black or bottle-green slag a malleable 
button with a copper-red fracture is produced. The 
presence of much lead occasions a slagging of copper, while 
iron, on the other hand, protects the copper. Arsenic and 
antimony aid in the collection of the copper, since the black 
copper is thereby rendered more fusible. 

The fluxes used in the smelting must be free from sul¬ 
phur. With an ore containing less than forty per cent, of 
copper, it may be made with fourteen argol and eight salt¬ 
petre ; with forty to fifty per cent, of copper, with sixteen 
argol and eight saltpetre ; and with fifty to seventy per cent, 
of copper, with twenty argol, and eight saltpetre. The 
more saltpetre is present the more does the copper incline 
to slag. 

Instead of the black flux—if this contains sulphur—a 
mixture of one hundred parts of pure carbonate of po- 
tassa, and ten to twelve parts of flour, is used. 

If black flux is used, the charge for one centner of ore 
consists of two and a half to three centner of black flux, 
twenty-five to fifty pounds of borax-glass, and fifty pounds 
or less of glass that is free from lead and arsenic. The ore 
is rubbed together in a porcelain or serpentine mortar with 
one-third of the black flux, placed quickly in a crucible, the 
other two-thirds of black flux added ; twenty-five pounds of 
borax, and thirty to fifty pounds of glass spread over it, 
the whole covered over with two to three centner of chloride 
of sodium, and on the top is laid a piece of coal about the 
size of a half inch cube. The upper layer of black flux 
prevents the ore from being thrown out of contact with it 


GERMAN COPPER ASSAY. 


323 


by the foaming up of the mass consequent upon the reduc¬ 
tion. If the piece of coal is taken too large, almost all the 
chloride of sodium soaks into it, and the assay is too much 
denuded of slag. In the absence of coal, copper is apt to 
slag. Difficultly fusible ores require a smaller addition of 
glass, as this itself is rather difficultly fusible. For the better 
collection of the copper* with richer ores, an addition of live 
to fifteen per cent, of arsenic is often given. If the ores 
contain sufficient lead, no addition of arsenic is required. 
An addition of as high as ten per cent, of iron, with ores 
that are poor in iron, is very useful both in the re¬ 
duction smelting and in the subsequent refining of the black 
copper. 

The presence of protoxide of iron is the safest means to 
obviate a slagging of the copper, and seems to prevent it to 
a greater extent, and with more certainty, than a change in 
the ratio of the saltpetre to the argol in the preparation of 
the black flux, or than the use of a lower and less prolonged 
temperature in the smelting. Since protoxide of iron is fre¬ 
quently already present in the roasted assay, an addition of 
oxide of iron in the smelting is not always necessary; but 
the more the proportion of copper in the assay sample in¬ 
creases, the more useful does such an addition prove ; so that 
no error is committed if an addition of from one half to an 
equal weight of pure oxide of iron, or forge scales, is given 
to every assay in the smelting, or the assay mixed before the 
roasting with pure pyrites. The latter diminishes also a loss 
of silver in the roasting. 

Federated experience has shown that oxide of iron pre¬ 
vents the slagging of copper, and, particularly by Wehrle, an 
addition of the same is recommended with substances rich 
in quartz. Dr. W. Fuchs has also drawn attention to this, 
and by his experiments is led to the conclusion, that a 
weight of protoxide of iron equal to that of the black flux, 
can unite with the potash of the black flux to a chemical 
compound of the formula 2FeO,KO, and that if so 
much oxide of iron is added to the assay that FeO,KO 
is formed, the copper is made secure from slagging; 
further, that by the addition of oxide of iron, the black 


324 


GERMAN COPPER ASSAY. 


flux (best made from two saltpetre and five argol) is 
rendered more fusible. 

Since it has long been known that fusing alkaline car¬ 
bonate is decomposed by oxide of copper, it must be ad¬ 
mitted that oxide of iron can separate oxide of copper from 
its combination with alkali, though this separation may not 
perhaps be wholly complete. 

The assays are exposed to a yellowish-white heat for half 
an hour to an hour in the muffle or wind furnace (in the 
Unterhartz, ore and matt assays are allowed to remain in 
the wind furnace thirteen minutes, and slag assays a quarter 
of an hour after the fire is well ignited), and when the 
muffle furnace is used, glowing coals are laid before the 
crucibles about half-way up to their tops. The contents of 
the crucibles must be completely fused. 

With an assay that has succeeded well (that is, with 
proper charging and temperature), neither the salt covering 
nor the slag is reddened with suboxide of copper. The slag 
is blackish-green from protoxide of iron, glassy, uniform, 
and easily snaps in pieces. With a red, and therefore cupri¬ 
ferous slag, either the temperature was too high or too long 
continued, or too little coal, or too much borax and glass 
present, or the assay too difficultly fusible, which last may 
be known from the appearance of the heterogeneous, porous 
slag. Unburned coal must remain on the salt, and at the 
bottom of the crucible must be found a well fused button 
of a red or more greyish colour, according to its purity. If 
there is found between the copper button and the slag a 
brittle crust or layer of matt, the roasting was not complete, 
and the assay is to be thrown away. 

Only when substances are to be examined which contain 
nothing but sulphides of iron and copper, and besides have 
but little or no earthy gangue, provided too that the quantity 
of copper is not very small, can a copper button be obtained 
by roasting and reduction smelting with a well-proportioned 
mixture, whose weight shall give the contents of the ore 
with sufficient accuracy. But the metallic button obtained 
must then, with a slag that is free from copper, have all the 
characteristics ot pure copper, must upon its surface, as well 


GERMAN GOITER ASSAY. 


325 


as in the fracture, be pure copper red, and be capable of 
being hammered without breaking or cracking. 

If the colour and malleability of the copper button prove 
that the impurities cannot amount to over one to three 
per cent, of the weight of the copper, a further refining is 
omitted on account of the loss thereby occurring. (Mansfeld 
copper matts.) 

All metallic oxides still present in the roasted assay 
sample, which are as easily reduced as oxide of copper, and 
whose metals are fusible at the temperature used, either by 
themselves or when alloyed with copper, pass into the 
copper as it separates out. In all cases, therefore, when the 
roasted assay still contains such metals, among which are 
lead, bismuth, tin, cobalt, nickel, antimony, arsenic, &c., 
there can be no pure copper produced, and the copper 
then obtained is designated by the name of black copper. 
This black copper must then, by a third operation, be 
freed from these foreign ingredients, to which, if the roast¬ 
ing was not exceedingly thorough, sulphur may also be 
added 

3 . The Refining of the Copper on the Cupel or on the Refining 

Dish. 

This operation aims at the removal of the foreign ingre¬ 
dients from the black copper. 

For this purpose the copper is brought to fusion, and 
access of air allowed. Thus the constituents of the black 
copper, which are more easily oxidised than copper, namely, 
phosphorus, sulphur, arsenic, antimony, lead, iron, bismuth, 
zinc, &c., are next converted into oxides, and may be removed 
as such. A partial oxidation of the copper at the same time, 
however, cannot be entirely avoided here; and, moreover, 
when it is attempted to prevent too great an oxidation of the 
copper, considerable traces of the substances named above 
are ant to remain behind in the refined copper. From 
other metals, namely, from gold, silver, nickel, cobalt, &c., 
the copper cannot be freed at all, or only imperfectly so, 
by this method. 


3 26 


GERMAN COPPER ASSAY. 


This is the reason of the imperfection of this mode of re¬ 
fining, and, therefore, of all methods of assaying which in¬ 
volve it. The most practised assayer, with all his skill and 
experience, cannot entirely remove this imperfection. This 
assay, however, none the less deserves to be used, for with 
acquired practice it yields a result in a shorter time , though 
it be but more or less approximately correct, than it is pos¬ 
sible to obtain one in the wet way. Moreover, rightly con¬ 
ducted assays, compared by the differences usually occurring 
between them, remain always, or nearly so, quite as reliable 
as many other metal assays in the dry way, e.g. the lead 
assay. 

The assay is in general considered as successful with rich 
and medium ores, when with correct management the 
weight of two duplicate assays does not differ by more than 
one per cent. 

This refining is performed in different ways. 

a. Befining upon the refining dish .—This method is the 
one most frequently chosen in Germany, e.g. at Freiberg, 
and at the Victor Frederic smelting-house, and also in Hun¬ 
gary. It is especially applicable when the black copper 
does not contain very much lead, and is the more reliable 
the purer the black copper already is. 

By this method indeed an oxidation of the copper can¬ 
not be wholly prevented, but under favourable" circumstances 
the loss thus occurring is vanishingly small. In Freiberg 
the copper button, with as little borax as possible, generally 
an equal weight, wrapped in a cornet of letter-paper, is 
placed on the very flat, white-hot dish, surrounded by glow¬ 
ing coals, and fused quickly at as high a temperature as 
possible. A slow fusion occasions oxidation and slagging of 
the copper. If black copper, which contains neither arsenic, 
antimony, nor lead, is to be examined, then to a fifty pound 
assay, five to ten per cent, of lead and thirty to fifty per cent, 
of borax, as may be required, are added, in which case the 
borax is generally fused first on the white-hot dish, then the 
copper, and afterwards the lead added. If the copper to be 
refined is not in a single piece, then, in order to avoid loss, 
it is never placed on the dish at the same time with the 


GERMAN COPPER ASSAY. 


327 


borax, but only after the intumescence of the latter has 
ceased. A black copper containing sulphur sparkles when 
placed on the dish. Cornets of weighed lead and borax must 
always be at hand to add in case of necessity. 

As soon as the copper shows a convex, perfectly clear 
surface, and is surrounded by a thinly fluid ring of borax 
slag, the mouth of the muffle is sligh tly opened to give access 
to the oxygen necessary for the oxidation. If the copper is 
not clear, but covered with a black crust, while at the same 
time the muffle is white hot, the operator tries adding borax. 
If this alone does not help the matter, a cornet of lead is 
added, and the heat increased, if possible, when the black 
copper soon presents a clear surface. Very impure black 
copper with only forty to fifty per cent, of copper, is placed oil 
the dish at first with a large quantity of borax only, without 
lead, and the latter added only when the copper is sufficiently 
refined. Special care must now be taken that the tempera¬ 
ture does not sink too low. If lead is present fumes of it 
rise at this period. A portion of the lead goes into the slag. 
Arsenic mostly passes off in fumes ; a portion of it, however, 
remains in the slag as arseniate of iron. Antimony behaves 
similarly, only it is more obstinately retained by the copper. 
Nickel is the most difficult to scorify, and can only be slagged 
by a large addition of lead, and in consequence of this, with 
a considerable loss of copper. If too little borax is present 
the slag is apt to become stiff, or solidify. 

When the copper is nearly refined, it ‘ brightens ’ like 
silver, only less distinctly; the 4 brightening 5 is particularly 
to be seen at the lower edge of the metal. In the presence of 
antimony and arsenic, the 4 brightening’ is less distinct than 
with lead, but it becomes so also with the latter when the 
buttons are small. In the latter case the assay is assumed to 
be done, when it no longer fumes. The temperature must, 
at the instant of 4 brightening,’ be exactly at the point at 
which the copper solidifies, since otherwise it would continue 
to oxidise; but good care must be taken that the copper 
does not solidify too soon. It shows in the 4 brightening ’ a 
peculiar green colour. The assay is now removed from the 
furnace, carefully quenched in water, and freed from the slag. 


328 


GERMAN COPPER ASSAY. 


The buttons should not differ by more than one to two per 
cent, in weight, and the value is stated only in whole pounds 
through all degrees of richness. 

In a good assay the button has the pure copper colour, is 
ductile, and uniformly granular and rose-red in the fracture. 

A button not sufficiently refined is red exteriorly, but the 
fracture is grey ; an over-refined one, dark red exteriorly and 
brittle, the fracture more smooth than granular, and with a 
high over-refining, even laminated, moreover, the slag is then 
red. With proper refining, the slag is blackish-green, from 
the presence of iron. If lead were present, the slag is greenish- 
blue at the edges from iron, nearer the button it is yellowish- 
red from PbO,Cu 2 0, and at the button itself suboxide of 
copper appears. The yellowish-red colour must not be con¬ 
founded with that of the basic arseniate of iron, which forms 
copper-red spangles on the surface of a slag that is saturated 
with it. Since the adding of lead involves an unavoidable 
loss of copper, an addition is necessary to the amount of cop¬ 
per found, in order to learn the correct contents of the black - 
copper. Empirically, to every ten pounds of metal slagged 
off (from the black copper and the lead added) one pound of 
copper is reckoned as also slagged. In many localities, for 
every five pounds of loss (of the black copper) one pound 
more of copper is reckoned. If there is a lack of borax in 
the refining, more may be added in the process. If the dish 
then becomes too full, it is cooled in water, the copper freed 
from the slag, and again mixed with borax on a new dish. 
But then a loss of copper is more apt to occur, as most of the 
iron, which otherwise protects the copper from slagging, is 
already slagged off. It is therefore sought in preference to 
get through with a single operation. 

If much arseniate of iron forms, which begins to make the 
slag stiff, no more borax can be added, as the assay is thereby 
completely chilled and cannot be again rendered fluid. In 
such a case the assay must be freed from the slag. A new 
addition of borax, therefore, should only be given in the com¬ 
mencement, while the slag is yet entirely fluid and the but¬ 
ton is not yet clear. When the button once becomes clear 
a further addition of borax is seldom necessary if the furnace 


GERMAN COrPER ASSAY. 


329 

is kept liot enough. Only very impure black coppers do 
not then refine with a single operation. 

Plumbiferous black copper is already copper-coloured, has 
a certain softness, and quickly refines. Arsenical black cop¬ 
per refines more slowly, requires more borax on account of 
the iron it contains, and never gives a refined copper of a 
fine red colour. So long as it is not yet refined, if the 
heat is high enough, it is movable on the dish. With very 
arsenical copper, if the heat is very strong, a blue arsenic 
flame bursts forth, which lifts the button. A constant blue 
halo of burning arsenic is often seen. 

Gold and silver remain in the copper, and must be taken 
account of, when they amount to one-half per cent. Much 
silver makes the copper white. Generally, only two assays 
are carried on at once; however, with proper attention, four 
assays may be made at the same time. 

b. Refining on the cupel .—This method has been in use at 
different places, e.g. at the Oberhartz and Unterhartz smelting 
works, since the time of Schliiter. It is by no means more 
accurate than the above, but is, perhaps, the most suitable 
one for very plumbiferous black copper. 

A quantity of pure copper equal in weight to the black 
copper is weighed out, while two cupels are brought to a 
white heat in the muffle of the assay furnace. Upon each 
of the cupels an equal weight of pure lead is placed, and 
when this has begun to ‘ drive,’ the black copper is placed 
on one cupel and the pure copper on the other, whereupon 
the muffle is again closed till the alloy on the cupel once 
more ‘ drives’ well. Sometimes (as at the Unterhartz) half 
of the lead is placed on the cupel with the copper, and as 
soon as this is red-hot, the other half of the lead added. 
The quantity of lead to be used depends upon the nature 
of the black copper; if this is very plumbiferous, an equal 
weight of lead may suffice; if the black copper is almost or 
entirely free from lead, and is also impure, two and a half 
to four parts by weight of lead must be added (at the 
Unterhartz, for example, four parts of lead are taken). 
During the 6 driving,’ in which the muffle is fully one half 
opened, without however closing the draught of the furnace, 


330 


GERMAN COPPER ASSAY. 


a sufficient heat is to be secured, and it must be especially seen 
to that both cupels remain equally hot, so that the purifica¬ 
tion of the copper may be as nearly equal as possible on 
the two. The higher the heat in the 4 driving,’ the purer 
does the copper become, and the rounder is its form. The 
4 brightening ’ of the assay is somewhat more distinct than 
in the refining on the refining dish. As soon as it has en¬ 
sued, a spoonful of coal-dust or borax is poured over the 
cupels in the muffle. They are then immediately taken out 
of the furnace and cooled in water. The indications of the 
refinement of the copper are the same as above ; it is diffi¬ 
cult, however, to obtain buttons wholly free from lead. The 
simultaneous and similarly conducted cupellation of a quan¬ 
tity of pure copper equal in weight to the black copper, with 
the assay, is intended to make a calculation possible of the 
quantity of copper, which the black copper has lost by scori- 
fication. What the pure copper has lost in weight is added 
to the weight of refined copper obtained from the black cop¬ 
per. An example will make this clearer. Let the black 
copper weigh seventy-five pounds. Seventy-five pounds then 
of pure copper may be cupelled with 75 x 3 = 225 pounds 
of pure lead, and sixty pounds of copper be recovered from it, 
so that the copper consumed has amounted to 75 — 60 = 15 
pounds. Let the black copper, likewise cupelled with two 
hundred and twenty-five pounds of lead, have yielded 
forty pounds of refined copper ; then the quantity of copper 
contained in the seventy-five pounds of black copper amounts 
to 40 + 15 = 55 pounds, which is the amount to be stated, if 
the black copper did not contain lead. If, however, the 
black copper is very rich in lead, a second correction is also 
made. The difference, 75 — 55 = 20 pounds, is considered 
as lead. Now, as in the assay with pure copper, two hun¬ 
dred and twenty-five pounds of lead have slagged fifteen 
pounds of copper ; these twenty pounds of lead are assumed 
to have slagged =1J pounds more of copper. The 
quantity of copper to be reported, therefore, amounts to 
40 + 15 + 1^ = 56^ pounds. 

If the black copper is so much contaminated with lead 
that by refining in the manner specified no copper would be 



GERMAN C01TER ASSAY. 


331 


obtained from it, an equal weight of pure copper is added 
to it, and a double weight of pure copper simultaneously 
cupelled upon the second cupel. For example, let the 
black copper weigh seventy-five pounds; then seventy- 
five pounds of pure copper are added to it, and cupelled 
with 2 x 75 x 3 = 450 pounds of lead. On the other cupel, 
75 x2 = 150 pounds of pure copper are cupelled with four 
hundred and fifty pounds of lead. The calculation is made 
as above, only the seventy-five pounds of copper added are 
finally again deducted. If the quantity of lead to be added 
is diminished, this must be done equally in the actual assay 
and the controlling one. 


b. Assays of Poor Ores and Products of Class I. 

1. Concentration Fusion. 

Five to ten centner and more of the unroasted ore are 
mixed with fifteen to twenty per cent, of iron pyrites free 
from copper, in case pyrites is not already present in the 
ore, and the assay smelted with an addition of fifty to one 
hundred per cent, of borax, under a thick layer of chloride 
of sodium in a clay crucible at an incipient white heat. 
By this process a button of crude matt is obtained, in 
which the copper of the assay sample is found concentrated 
as sulphide of copper. This crude matt is weighed, and 
then first subjected to a copper assay by roasting, reduction 
smelting, &c. If several assay centner have been taken for 
the concentration smelting, the final proportion of copper 
found is calculated accordingly. 

A slagging of copper is indeed seldom entirely avoided by 
this concentration smelting, but the loss of copper is gene¬ 
rally less than if such poor ores were at once, without any 
previous work, subjected to the ordinary process in the dry 
way, which would sometimes yield no button of copper at 
all, since the little copper in the ore is lost in the slag. 

According to Fuchs, for the most complete preven¬ 
tion possible of a loss of metal, and for the purifying of the 


332 


THE ASSAY OF COPPER. 


copper, tlie well roasted ore is placed in an assay crucible 
while still hot, with twenty per cent, of pyrites and twenty 
per cent, of sulphur, covered with powdered glass and 
some vitrified borax, and smelted to matt. 

2. Fusion with Collecting Agents. 

With poor and impure ores, if the ordinary method is 
used, errors are very apt to arise, from the infusibility of the 
ore and from the basic nature of the suboxide of copper, 
which, especially in the presence of silica, is very much in¬ 
clined to slag. In such cases, as practised in Freiberg, lead, 
litharge, arsenic, antimony, arsenious acid, or oxide of anti¬ 
mony, is added for the collection of the copper while smelt¬ 
ing to black copper. These fluxes have their advantages 
but also their disadvantages. Five to fifteen per cent, of 
lead or litharge gives with copper an easily fusible alloy, 
which collects better together, but also carries copper into 
the slag, which consequently becomes red. If the result of 
experience is taken as a basis, that, in the refining smelting, 
ten pounds of lead slag one pound of copper, then if five 
per cent, of lead are added to an ore with one per cent, of 
copper, only half a pound of copper is obtained, and with 
thirty per cent, of lead no copper at all would be obtained. 
The intimate mixture of the lead with the ore has also its 
difficulties, and therefore it is better in this connection to 
use litharge. 

By an addition of arsenic , antimony , arsenious acid , or 
oxide of antimony , easily fusible compounds of arsenic and 
antimony with copper are obtained, the mixing can be ac¬ 
complished more thoroughly than with lead, and for poor 
ores, such an addition is more suitable than one of lead. On 
account of danger in dealing with arsenious acid, it is best to 
use metallic arsenic, which does less harm in the refining 
than antimony. In this operation, indeed, neither of the 
two is entirely removed from the copper, and they impart 
some brittleness to it, and a greyish colour to the fracture. 
The assayer may, however, be satisfied with the result of an 
assay treated with arsenic 


TIIE ASSAY OF COPPER. 


333 


c. Assays of Oxidised Ores and Products of Class II. 

Oxidised copper ores and products are — 

1. Without previous roasting, subjected to a solvent and 
reducing fusion, and the black copper thus produced, refined, 
if necessary (richer ores and products, e.g. red copper, 
malachite, refinery slags, &c.). 

2. After previous roasting, smelted to black copper, (e.g. 
sulphate of copper, copper ores which contain arsenic acid, 
antimonic acid, &c., ores imperfectly roasted in the large 
way, many copper ore slags, cement copper slimes, which 
may contain basic sulphate and arsenate of iron, &c.) The 
roasting is performed with an addition of coal-dust or 
graphite, and finished, if necessary, with carbonate of am¬ 
monia. 

3. Smelted to black copper with collecting agents (lead or 
arsenic). Poor oxidised copper ores, especially the quartzose 
ones, must always be treated in this way. For example, poor 
copper ore witli chalybeate and basic gangue without silica 
is mixed with ten per cent, of arsenic, thirty to forty per 
cent, of borax, and twenty to twenty-five per cent, of glass; 
if it contains pyrites, mispickel, quartz, and calcspar, with 
twelve per cent, of arsenic, thirty per cent, of borax, and 
thirty per cent, of glass, besides black flux; ferruginous, 
quartzose malachite, with ten per cent, of arsenic, sixty per 
cent, of borax, and fifteen per cent, of glass. If poor oxi¬ 
dised ores are free from iron, ten to twenty per cent, of 
oxide of iron is added. Also richer oxidised substances are 
advantageously mixed with collecting agents, e.g. refining 
slag, with five per cent, of arsenic, thirty per cent, of borax, 
and thirty per cent, of glass. 

4. Subjected to a concentration fusion, with twenty to 
twenty-five per cent, of pyrites free from copper and twenty 
per cent, of sulphur, one hundred per cent, of vitrified borax, 
one hundred per cent, of glass, and twenty to twenty-five 
per cent, of colophony with a covering of salt, and the re¬ 
sulting matt treated like a sulphuretted ore. The ore is 
placed on top of the pyrites and sulphur, and covered over 
with the fluxes, &c. 


334 


THE ASSAY OF GOITER 


d. Copper Alloys. Class III. 

But very few copper alloys can be refined by the above 
process. For the black copper produced by the copper 
smelting process, everything is observed which was pre¬ 
scribed for the refining of the buttons resulting from the 
reduction smelting. If the refining is to be done on the 
cupel, one or more rarely two centner are weighed out for 
the assay. Cupriferous lead is refined on the cupel. Two 
centner of the cupriferous lead and half a centner of pure 
copper are placed on one cupel, and on the other, two cent¬ 
ner of pure lead, and half a centner of pure copper, and the 
two are cupelled at an equal heat. If now, for example, 
thirty-six pounds of copper have been obtained on the first 
cupel, and twenty-seven pounds on the second, then in the 
two centner of the assay substance there were contained 
36 — 27 = 9 pounds, or four and a half per cent, of copper. 

Heine gives for the examination of the Mansfeld black 
copper , which seldom contains more foreign ingredients than 
four to seven per cent, of iron, a little sulphur, and only 
traces of zinc, cobalt, nickel, lead, and phosphorus (the whole 
amount of the substances last named is not generally over 
one per cent.), the following directions :— 

One or half an assay centner of the black copper in filings 
is weighed out in duplicate, and placed in the muffle, at first 
with a gentle, then with a stronger heat, and with frequent 
rubbing up, until all the copper appears black and changed 
to oxide, and no more grains can be felt with the pestle. The 
roasted assay is now mixed with two to three centner of 
black flux and one to one and a half centner of glass, free 
from lead and arsenic, the charge placed in a crucible for 
assaying copper, covered with salt, and smelted in the wind 
furnace. The black flux for this assay must consist of at 
least twenty parts of argol to eight parts of saltpetre, since 
with a smaller quantity of argol red slags are generally pro¬ 
duced. Should this still be the case, six to eight assay 
pounds of coal-dust are added to the charge. Heine obtained 
in this way a copper, which he considered quite as well re¬ 
fined as that produced by the preceding processes. 


THE ASSAY OF COPPER. 


335 


These directions may, perhaps, deserve to be followed 
with black copper similar to this, as they allow us to dis¬ 
pense with the always imperfect refining on the cupel or 
refining dish ; especially if, for reasons already explained, a 
portion of pure oxide of iron or forge scales is mixed with 
the roasted assay in the smelting, in order the more certainly 
to avoid the formation of a red slag, which always indicates 
loss. 

The most frequent alloys of copper, i.e. brass , German 
silver, gun metal , &c., cannot be assayed in a reliable manner 
in the dry way. German silver, because the nickel could 
not be removed at all, or only with great difficulty, and the 
rest because zinc and tin give such difficultly fusible oxides, 
that they could not be properly removed in the refining. 

In the alloys of copper with silver, gold, and platinum, the 
copper may be determined from the loss arising from cupel- 
lation with lead. 


Remarks upon the Copper Assays in the Dry Way . 

These assays are burdened with various defects. The 
roasting is an exceedingly tedious process, and only by a 
gradually increasing temperature, by repeated grinding up 
and mixing of the roasting substance with coal-dust, graphite, 
or carbonate of ammonia, is it possible to sufficiently remove 
the sulphur. In the reduction smelting, loss of copper is apt 
to occur, if a correct temperature and a suitable charging are 
not employed. If the fluxes (borax, glass, &c.) are present 
in too large quantity, copper is slagged ; if there is a lack of 
them, a very impure black copper is produced, with whose 
diminishing richness in copper, the loss of copper in the re¬ 
fining increases. The last-mentioned operation is in and of 
itself imperfect, and on account of the high temperature it 
requires, and the ever necessary attention of the assayer, very 
troublesome. 

The poorer the substance is in copper, the more unreliable 
do the results of the assays become. 

In all docimastic assays of copper in the dry way, the 
silver or auriferous silver contained in the assay sample 


33 n 


TIIE ASSAY OF GOITER. 


cannot be removed, and it has generally pretty completely 
collected in the copper obtained. These copper assays give 
nowhere any indications whether gold or silver is present or 
not; and the amount of these metals which may be present 
must therefore be both sought for and determined by a 
special assay for them. If they are found, and in sufficiently 
large quantity, they are deducted from the weight of the 
copper. 

The dry assay is mostly found in practice in smelting 
works, where even in the hands of less scientifically educated 
than skilful assayers, with the character of the assay sub¬ 
stance once known, and suitable practice in following out 
the separate manipulations, it gives results which suffice for 
the business of working copper in the large way. 


B. ASSAYS IN THE WET WAY. 

I. For Substances rich in Copper. 

a. kerl’s modified Swedish assay. 

One assay centner of finely rubbed ore, &c., is warmed in 
an assay flask or beaker, on the sand-bath, with as little as 
possible of aqua regia (two parts crude hydrochloric, and 
one part crude nitric acid), and as soon as the proper de¬ 
composition of the assay substance has taken place, in order 
to expel the nitric acid, evaporated nearly to dryness with a 
few drops of oil of vitriol. In the presence of nitric acid 
the copper would be only imperfectly precipitated by iron ; 
the presence of hydrochloric acid does no harm. Also the 
nitric acid may be destroyed by heating the solution con¬ 
taining it with crystals of protosulphate of iron, only the 
work then passes off less cleanly than if sulphuric acid is 
used. 

The still damp mass is cautiously moistened with hot 
watei, and filtcied into a beaker, the residue no longer con¬ 
taining any particles of ore, &c., is washed out a few times 
with boiling water (till a drop of the washings no longer 


THE ASSAY OF COPPER. 


337 


deposits a brownish coating of copper on a clean iron wire), 
the filtrate, about 150 to 160 cubic centimetres, heated 
nearly to boiling with a few pieces of iron wire about two 
inches long and two lines thick, till a brownish coating no 
longer forms on a clean iron wire held in the solution. The 
approximation to this point is indicated by the solution’s 
becoming colourless. Should the mass become dry in the 
evaporation with sulphuric acid, it is moistened before fil¬ 
tering with a lew drops of sulphuric acid, in order to make 
the basic salts formed soluble. The concentrated solution 
is not filtered on to the pieces of iron wire, but these are 
placed in the solution after it is diluted with the washings, 
because otherwise they become so rapidly and so firmly 
coated over with copper, that the latter can only with diffi¬ 
culty be separated from them. The pieces of wire are so 
taken as to correspond in size with the beaker used, and of 
such a length as to cross one another in it, in order to pre¬ 
sent as much surface as possible to the direct contact of the 
fluid. 

After the precipitation is ended, the beaker is poured full 
of hot water, which, after some time, is decanted, care 
being taken that no copper goes with it, the beaker again 
filled with hot water, a porcelain saucer placed bottom 
upwards on the top of it, and beaker and saucer then in¬ 
verted so that the iron wires, together with the copper and 
some of the fluid, sink into the saucer. When this has 
taken place completely, the beaker is removed from the 
saucer by drawing it quickly over the side with the hand, 
the iron wires freed by rubbing them with the fingers 
from the copper coating, which does not adhere firmly, well 
rinsed off, and the copper well washed two or three times 
by decantation with hot water. The decanted fluid may be 
placed in a beaker, and allowed to stand quiet for some 
time, that it may again deposit any very finely divided 
copper suspended in it. The latter is not to be confounded 
with the particles of carbon separated from the iron wires, 
and which pass off in part in the decanting. Owing to the 
short time occupied by the precipitation of the copper, few 
or no particles of carbon and iron are detached from the 

z 


338 


TIIE ASSAY OF COFPER. 


wires, as in the older assays, and the copper is precipitated 
with a pure metallic colour, without being in the least conta¬ 
minated by basic salts of iron. 

The damp copper, freed from water as much as possible 
(if necessary, by removing it with blotting-paper), is dried at 
a gentle heat in an atmosphere freed from acid vapours until 
two successive weighings give the same result. An oxida¬ 
tion of the damp copper may be counteracted by adding 
alcohol to it, and also by covering over the saucer. Over¬ 
much care in the drying is not required, for even at a 
somewhat higher temperature the increase in weight is but 
very small, so long as the copper retains its proper colour. 
The precipitated copper should not be allowed to remain 
too long in contact with free sulphuric acid, since it is oxi¬ 
dised by it. 

This process alone can only be used •when in the sub¬ 
stance to be examined there are no other metals present 
(tin, antimony , arsenic , gold , bismuth) which are likewise 
thrown down by iron. Silver , lead , and mercury are indeed 
also precipitated by iron, but these metals can be readily 
removed. Silver and lead remain in the insoluble residue, 
the first as chloride of silver, and the last as sulphate of lead, 
and may be determined by assaying it after incinerating the 
filter. Mercury (contained, for example, in many fahlerzen) 
is indeed thrown down with the copper, but is volati¬ 
lised by igniting the copper in a porcelain crucible or on a 
roasting dish in the muffle, whereby the copper also passes 
into pulverulent black oxide, and after two ignitions is 
weighed as such. One hundred parts of oxide of copper 
contain 79*826 of metallic copper. The oxidation may be 
promoted by moistening the copper with nitric acid before 
ignition. 

The so-called copper slate (Kupferschiefer) must, before 
treating with aqua regia, be ignited to remove the bitumen. 
If the substance cannot be completely decomposed by aqua 
regia (many slags , for example), it is first fused in the finely 
pulverised state, with about two to two and a half parts of 
carbonate of potassa, or calcined carbonate of soda, in a clay 
crucible at a red heat in the muffle or in a platinum crucible 


THE ASSAY OF COPPER. 


339 


over a spirit-lamp. If the assay sample contains lime , diffi¬ 
cultly soluble sulphate of lime is formed, which may, how¬ 
ever, be dissolved out by repeatedly washing the copper 
with boiling water. 

The presence of iron , nickel , cobalt , manganese , and zinc 
in the assay substance does no harm, as their sulphates are 
not decomposed by iron. 

While by the older method an assay might last from one 
to two days, during which time, indeed, as many assays 
might be simultaneously conducted as the arrangements 
otherwise allowed, all the operations of this newer method 
require but from two and a half to three hours, with an ore 
containing tw T o to seventy per cent, and more of copper. 

With respect to the accuracy of the assay, with suitable 
substances, as the experiments at the Oberhartz smelting- 
house and the investigations of Yon Hubert have proved, it 
leaves nothing more to be desired as a business assay. At 
the smelting-house alluded to, the different assayers are 
allowed two per cent, difference, which is, however, very 
large. 

Mohr has given an analytical accuracy to this assay, by 
performing all the operations as much as possible in the 
same vessels, conducting the washing with care, and preci¬ 
pitating the copper with granulated zinc free from carbon, 
instead of using iron, which liberates coal. As a business 
assay, however, the Oberhartz method is to be preferred on 
account of its simpler practicability. 

If bismuth , gold , tin , antimony , or arsenic are present in 
the substance to be assayed, the method described requires 
different modifications according to whether arsenic is pre¬ 
sent or not. The presence of bismuth , which, moreover, 
seldom occurs ( e.g . in many jalderzen, cupreous bismuth ), 
also necessitates a special assay treatment. 

a. Arsenic is not present. One assay centner of the ore, 
&c., is decomposed at a more or less high temperature by 
nitric acid, so that gold , oxide of antimony , and oxide of tin , 
remain in the residue, as also silver , if some chloride of 
sodium is added to the solution. It is now filtered, the 
precipitate washed with water, the filtrate evaporated, to 


340 


THE ASSAY OF COPPER. 


expel the nitric acid, and to separate any lead that may be 
present, with sulphuric acid, and the copper precipitated 
from the filtrate in the usual way. Mercury, it present, is 
removed in the manner stated above. 

b. Arsenic is present One assay centner of ore is decom¬ 
posed in a beaker or a roomy flask with as little aqua regia 
as possible, the free acid neutralised with soda, or even 
supersaturated so that a precipitate separates, and the mass 
digested with excess of solution of sulphide of sodium for 
some time (perhaps half to three quarters of an hour) at 
almost boiling-heat. The solution of sulphide of sodium is 
prepared by igniting and lixiviating a mixture of two parts 
of anhydrous carbonate of soda and one part of coal-dust or 
flour. To the filtered solution of this salt flowers of sulphur 
are added in excess, which partially dissolve in it and 
increase its capacity for dissolving the electro-negative sul¬ 
phides of gold , antimony , arsenic , and tin , by forming with 
them sulphur salts, while silver , lead , copper , mercury , iron, 
zinc, manganese , nickel , and cobalt are sulphurised by the 
solution, but not dissolved. The two groups of metallic 
sulphides are separated by filtering, and the sulphides of the 
last group, which remain on the filter, well washed with 
cold water. The finger is then held over the bottom of the 
funnel, concentrated nitric acid poured on the filter, and the 
sides of the funnel carefully heated by slowly revolving it 
over a spirit-lamp. The sulphides thus partially dissolve in 
the acid, but separate completely from the filter, so that by 
punching a hole through the bottom of it they can without 
difficulty be washed into a beaker. Here they are com¬ 
pletely decomposed by heating with the nitric acid, the 
latter removed with simultaneous separation of the lead, by 
heating with sulphuric acid, and the process continued as 
heretofore prescribed. 

c. Bismuth is present . After gold, antimony , arsenic , and 
tin have been removed, if necessary, in the manner pre¬ 
scribed under a or b , carbonate of ammonia in excess is 
added to the solution obtained, which contains copper and 
bismuth. By this the copper is dissolved, while bismuth , 
lead , and mercury are precipitated as carbonates. After a 


THE ASSAY OF COFFER. 


341 


while the blue copper solution is filtered off, the carbonate 
of ammonia supersaturated with sulphuric acid, and the 
copper precipitated from the solution with iron. Should 
much iron and alumina be contained in the solution that 
has been freed from gold, antimony, arsenic, and tin, then 
in the precipitation with carbonate of ammonia a slimy pre¬ 
cipitate is formed which may retain much copper. In such 
a case the solution is evaporated with sulphuric acid, and 
the copper precipitated in the usual way with iron. Since, 
however, the copper then contains bismuth and mercury, it 
must be redissolved in nitric acid, and the solution treated 
as above with carbonate of ammonia. 

Synthetic experiments with substances of most varied 
composition have proved that this modified assay yields 
sufficiently correct results as a docimastic assay with ores 
containing two to seventy per cent, and more of copper. 
Either the precise percentage of copper weighed out is 
again obtained, or with the richer ores a difference of at 
most two per cent, occurs between several assays of one and 
the same kind. 

By means of the Oberhartz assay and Heine’s colorimetric 
assay the copper contents of all substances, rich and poor, 
can be docimastically determined with sufficient accuracy. 
By the Oberhartz assay, proportions of two to three per 
cent, and over are determined, and by Heine’s mode the 
lesser ones down to *03 per cent. 

b. ASSAY OF COPPER BY PRECIPITATION WITH METALLIC ZINC. 

The precipitation of copper from its solutions is of old 
date. Fresenius recommends the process, the accuracy of 
which he has tested, in his 4 Quantitative Chemical Analysis.’ 
The process is performed in the following manner. The 
solution, either in hydrochloric or sulphuric acid (nitric acid,' 
if present, must be expelled by evaporation with sulphuric 
acid), is transferred to a weighed platinum dish, diluted so as 
to ensure a moderate and steady evolution of gas, and a 
piece of pure zinc introduced. The dish is covered with a 
watch-glass, which is afterwards rinsed into the dish. Heat 


342 


THE ASSAY OF COFFER. 


promotes the reaction, but is not strictly necessary. The 
copper is deposited partly as a coating upon the platinum, 
partly in the form of spongy masses. Sufficient acid must 
be always present to maintain the evolution of hydrogen. 
In about an hour or two, all the copper will have separated: 
a few drops of the solution must be tested with sulphuretted 
hydrogen water to make this certain. If no colour has been 
imparted to the solution, it may be assumed that all the cop¬ 
per has been deposited. The metal in the dish is now examined 
for undissolved zinc by pressing with a glass rod, and by 
addition of hydrochloric acid. All the zinc being dissolved, 
the copper is pressed together with the glass rod, the super¬ 
natant fluid decanted, and hot water poured into the dish 
and repeatedly decanted, without loss of time. The wash¬ 
ing is continued until the decanted fluid is quite free from 
hydrochloric acid. When such is the case, the water is 
decanted, as far as practicable, rinsed with alcohol, and 
dried upon the water-bath: as soon as the dish is cool, it is 
weighed. The precipitation can be effected in a porcelain 
or glass dish, though the process will occupy more time, 
and the copper will be deposited in non-adherent spongy 
masses. 

C. COLORIMETRIC COFFER ASSAYS. 

These are based upon the fact that ammonia added in 
excess to the solutions of salts of copper, produces a beautiful 
azure blue colour, whose intensity depends upon the quan¬ 
tity of copper dissolved. By comparing the shades of blue 
colour in equally thick layers of the dissolved ammoniated 
assay substance (assay fluid) with a normal or standard am¬ 
moniated fluid whose copper contents are known, the quan¬ 
tity of copper in the former can be calculated when its volume 
is measured. 

To Heine, the superintendent of the smelting works in 
Mansfeld, belongs the merit of having first successfully 
employed this reaction for the determination of small per¬ 
centages of copper, and later it has been also extended by 
Jacquelain, Von Hubert, and Muller, to the determination 
of larger quantities of copper. 


THE ASSAY OF COPPER. 


343 


1. Heine’s Colorimetric Method. 

For the docimastic determination of the quantity of 
copper in bodies poor in this metal, e.g. in slags, lead matte, 
litharge, crude lead, and other plumbiferous metallurgical 
products, tin, cupelled silver, &c. ; in short, in all sub¬ 
stances which contain from a trace to about one per cent, or 
a little more of copper, this method is the most advanta¬ 
geous to be used. 

After the assay sample has been reduced to as fine a state 
of mechanical subdivision as possible, which with slags is 
best attained by sifting or washing them, one centner (3-4 
grammes) of it is weighed out and dissolved or so fully de¬ 
composed by a suitable acid that in the residue, which is to 
be filtered and well washed, no more copper remains behind. 
For this purpose nitric acid or aqua regia is employed, accord¬ 
ing to the character and peculiar behaviour of the substance, 
and the nitric acid is concentrated or somewhat diluted, as 
may be required. The solution is either immediately, or after 
the copper has been first precipitated by hydro-sulphuric 
acid gas or iron and again dissolved, strongly supersaturated 
witli caustic ammonia, and the precipitate, if any, thereby 
produced, steeped in the caustic ammonia for a considerable 
time, and with frequent stirring at a very gentle heat (30°- 
40° C.), then filtered off and thoroughly washed. According 
to the quantity of copper present, and according to the 
degree of dilution, will the solution obtained, which if it 
should become at all turbid must be once more quickly 
filtered (e.g. with refined and crude lead), appear more or 
less strongly coloured blue. The volume of the solution is 
measured in graduated vessels, and the intensity of the colour 
compared with and determined from fluids, which have been 
previously prepared as standard fluids, and which, for a 
definite volume, contain a definite, accurately weighed quan¬ 
tity of copper, that has been dissolved in nitric acid, pre¬ 
cipitated by caustic ammonia, and redissolved in excess of 
the same. From the measured volume, and the intensity 
found by comparison, the quantity of copper is then de¬ 
termined by calculation. 



344 


THE ASSAY OF COITER. 


Heine proposes standard fluids with one, two, three, and 
four assay loth of copper in one ounce (two loth, commercial 
weight) of the ammoniated fluid. These four standard fluids 
are all-sufficient. 

If the French weights and measures are used, standard 
fluids are taken with -001 -002 *003 -004 grammes of copper 
to every twenty-five cubic centimetres of the fluid. 

The graduated vessels (cylinders) required for the prepa¬ 
ration of the standard fluids, as well as for the measuring of 
the assay fluid, can be easily prepared by the assayer himself. 
One quarter of an ounce of water is weighed out a number of 
times in succession and poured into the cylinder, and each 
time the height of the fluid is marked in a durable manner 
on the glass with a diamond, or by etching it with hydroflu¬ 
oric acid vapours, etc. Also earthen or porcelain measures, 
that are prepared and marked for the volumes that hold one, 
two, three, four, &c., ounces of water, may be used. 

It is not practicable to replace the volumetric measure¬ 
ment by weighing, for the quality and quantity of those 
substances which are soluble in acids and not precipitated by 
ammonia, or are again dissolved by it, may vary greatly in 
the assay. 

In the formation of the normal fluids, two assay pounds 
of chemically pure (galvanic) copper are weighed out on a 
good balance, dissolved in nitric acid, the solution super¬ 
saturated with caustic ammonia, and placed in a graduated 
cylinder, which is divided to whole, half, and quarter ounce 
volumes of water, and then water enough is added to bring 
the fluid to the sixteen ounce mark. The fluid then con¬ 
tains ft=4 loth of copper per ounce. Six ounces of this 
four loth solution are then taken, two ounces of water added 
to it, and eight ounces of fluid obtained, with 2 ¥ 4 = 3 loth of 
copper to one ounce of water. The two loth solution is 
formed in a similar way by diluting four ounces of the four 
loth solution to eight ounces ; the one loth, by diluting four 
ounces of the four loth normal fluid to sixteen ounces. In 
the measuring of the assay fluid it is estimated within one- 
eight of an ounce, which is sufficiently close. If in the 
dilutions a mistake is actually made of one-sixteenth of an 


345 


THE ASSAY OF COPPEIt. 

\ 

imuR ppagyf » ' •_ 

ounce, the maximum of possibility, the error-^m^ta^s to 
about two cubic centimetres, which in a whole mass of fluid 
of 200—500 cubic centimetres has no influence upon the 
solution that can be detected with the eye. 

The preservation of the standard fluids, as well as the com¬ 
parison of the blue assay fluids with them, must take place in 
glass vessels closed with ground glass stoppers. These ves¬ 
sels must have the same form and size, consist of the same 
colourless glass, and have an equal thickness of glass in the 
smooth side walls. The last condition is obtained the surest 
by grinding. This grinding, however, which notably in¬ 
creases the cost of the glasses, is not indispensably necessary 
if the vessels are carefully formed and blown in a good glass¬ 
house. An oblong form is most advantageous for the vessels. 
They hold about an ounce and a half of fluid, and are about 
two inches long, two and a half inches high, and one inch 
wide, with walls about one-eighth of an inch thick. 

The glasses are very advantageously formed from an un¬ 
blemished sheet of plate glass of equal thickness throughout, 
either by fusing or cementing the sides together and the 
insertion of a glass or platinum neck. The assayer has in the 
form of vessel indicated a triple control in the comparison of 
the assay fluid with the normal solution according as lie 
looks through the fluid in three different directions. 

The digestion of the assay sample with acid may take 
place in any suitable vessel whatever, a glass flask, a beaker 
covered with a watch-glass, &c., only no thumping and spirt- 
in^ of the fluid should be possible in the process. The nitric 
acid, &c., must be added little by little. The time required 
for this may vary greatly. The solution of cupelled silver * 
shimmings , &c., with nitric acid is finished in a short time; 
on the other hand, in the examination of difficultly decompos- 
ible slags, with which concentrated nitric acid or aqua regia 
wdll always be used, the digestion often requires to be con¬ 
tinued in a warm temperature for two to three times twenty- 
four hours. The mass must be frequently stirred with a 

* With cupelled silver, after dissolving in nitric acid, the silver may he 
precipitated with chloride of sodium, the chloride of silver filtered, washed, 
and the solution then mixed with caustic ammonia. 


34 G 


TIIE .ASSAY OF COPrER. 


glass rod, because many slags decompose rapidly with evolu¬ 
tion of heat, form a thick jelly, and deposit a crust on the 
bottom of the glass. Sub-, singulo-, and bi-silicate slags, 
mostly decompose readily, higher silicates resist complete 
decomposition by aqua regia, and then a preliminary solvent 
ignition or fusion with carbonate of potassa or calcined car¬ 
bonate of soda ; or better, a mixture of both, is necessary, 
precisely in the manner given in the wet assay of copper. 
Here also it does no harm if some of the substance of the 
crucible remains adhering to it. 

The decomposition of the slags by acid is complete 
when in the stirring with a glass rod no more grating can 
be perceived. 

After hot water has been added to the decomposed assay, 
the residue is collected on a filter, well washed out, with¬ 
out diluting the filtrate too largely, and the copper pre¬ 
cipitated from the solution, if necessary, with hydrosulphuric 
acid gas, especially when a notable quantity of alumina and 
iron is present, whose slimy precipitates from the immediate 
precipitation with ammonia always retain copper. This 
precipitation of the copper has also the advantage that, as 
cobalt and nickel do not precipitate with it, the colouring 
effects which they would produce, if present, are removed. 
Since the sulphide of copper requires for its solution but a 
few drops of nitric acid, in the succeeding treatment of the 
solution with ammonia, but a small quantity of ammoniacal 
salt is formed, and the specific gravity of the coloured fluid 
varies but very little from that of water and the normal 
solution. With the increase of the specific gravity of the 
assay solution, its volume is considerably increased, and 
therefore it gives too large a measure in the direct pre¬ 
cipitation with ammonia. If the precipitation with hydro- 
sulphuric acid gas is completed in four to six hours, the 
sulphide of copper is filtered out, thoroughly washed with 
cold water containing hydrosulphuric acid, the filter dried, 
ignited in a porcelain crucible, the oxide of copper formed, 
warmed with a few drops of nitric acid or aqua regia, 
supersaturated with ammonia, filtered, and well washed, till 
the washings are no longer tinged bluish. 



TIIE ASSAY OF COFFEE. 


347 


A precipitation of the copper with iron wire, from a 
solution evaporated with sulphuric acid, and a re-solution 
of the copper in nitric acid, consumes less time. If the 
copper is not previously precipitated, errors of some thirty 
per cent, and more of the whole amount of copper may 
occur. By repeated solution of the iron precipitate and 
precipitation with ammonia, all the copper cannot, however, 
be extracted. 

In the examination of litharge , the solution in nitric acid 
may be dispensed with. The oxide of copper can be at 
once extracted from it with caustic ammonia; however, the 
litharge and ammonia must then be allowed to work at 
least twenty-four hours on each other, with very diligent stir¬ 
ring, and, moreover, the litharge must be rubbed very fine. 

The ammoniacal solution obtained from the assay is now 
well stirred, so that it may mix with perfect uniformity 
with the last washings ; then, either the whole, or a part 
of it, is placed in a clean assay glass, and compared with the 
standard fluids in similarly formed glass vessels standing on 
a sheet of white paper. Should it correspond with none of 
them in the intensity of its colour, the whole of the fluid is 
diluted somewhat with water, until this is the case. Its 
volume is thereupon measured in the glass vessel graduated 
to ounces, &c., and noted. For a check, the dilution may 
be carried still farther till the colour of the assay corresponds 
to the next more faintly coloured standard fluid, and then 
the increased volume be measured anew. This might per¬ 
haps be still again repeated, but it becomes more and more 
uncertain. The calculation of the percentage of copper 
from the intensity and the volume found, then presents no 
further difficulty. 

Suppose that the assay fluid agrees with the normal solu¬ 
tion of four loth of copper to the ounce of water, and its 
quantity amounts to five ounces, then the quantity of copper 
in the centner of the assay substance is 5x4 = 20 loth. 
This fluid further diluted till it equals the normal solution 
with three loth of copper, must measure six and two-third 
ounces if the obtained value of twenty loth is to be con¬ 
firmed. 


348 


THE ASSAY OF COFFEE. 


According to Heine’s experiments, the possible error of 
observation in the comparison and measurement described, 
amounts as a maximum with the stronger normal solutions 
(with sixteen loth and over) to three quarters to one loth, 
with the weaker ones to scarcely half a loth of copper. In 
a centner of the assay substance, one loth of copper *03 per 
cent, can still be determined with certainty. 

Le Play determined in finely pulverised and carefully 
washed copper slags, the copper in one gramme of the poor¬ 
est slags to within half a milligramme, and of the richest 
slags to within one milligramme, by using twenty-six 
standard fluids with various percentages of copper in 
cylindrical vessels. The comparison of colours in round 
vessels is more uncertain than in oblong ones, since in the 
former the light is dissipated and shadows are produced. 

If a substance contains so little copper that the fluid 
does not equal the most faintly coloured standard fluid in 
intensity of colour, the assayer must endeavour to remedy 
the matter by evaporating till this is the case. An evapora¬ 
tion is, however, avoided, if possible, first because of the 
loss of time, and also because other precipitations, carbonate 
of lime, &c., are apt to be caused by it, and because, when 
it has to be continued too long, so much ammonia is very 
apt to be volatilised, that a new addition of it becomes 
necessary. 

This method of assaying soon finds the limits of its accu¬ 
racy in an increasing percentage of copper in the assay 
sample, since with fluids rich in copper and therefore 
strongly coloured blue, the errors of observation soon amount 
to several loth. And to seek then to better oneself by 
diluting largely, yields no more accurate results, since a 
small error of observation in determining the intensity of 
the colour, is so much the more multiplied in the calculation 
of the value by the greater number of the ounces. 

If nickel is contained in the assay substance, the assay 
cannot be conducted in the way prescribed, since the nickel 
is extracted by the acids, and dissolves also in caustic am¬ 
monia with a blue colour. The assay may also become 
uncertain from the presence of much manganese , cobalt , or 




THE ASSAY OF COPPER. 


349 


chromium , since they render the hue of the blue colour 
dingy. Chromium may be completely removed by a slight 
boiling of the ammoniacal fluid; not so cobalt. The pre¬ 
sence of vanadium or molybdenum does no harm. 

It nickel , or much cobalt and manganese are contained in 
the assay substance, the solution obtained by acids and 
filtered, though not further diluted, must first be decomposed 
by metallic iron. What is thrown down by the iron is 
collected on a small filter, washed thoroughly* and then, 
together with the filter, treated with dilute nitric acid. 
When the copper is all dissolved, this solution is supersatu¬ 
rated with caustic ammonia and then managed as above. 
With higher percentages of copper the process of the 
Swedish copper assay is used for determining the value. 
The precipitation of the copper may also be performed with 
hydrosulphuric acid gas. 

Le Play removes the injurious influence of manganese, 
nickel, and cobalt, by allowing the green or violet-coloured 
ammoniacal solution to stand open to the air for several 
weeks in a moderately warmed drying furnace, whereby 
a few variously coloured gelatinous flocks are gradually 
deposited, and the fluid, after the addition of a few drops of 
ammonia, then becomes pure blue. 

According to Jacquelain and Von Hubert, nickel and 
cobalt are in a simple way rendered perfectly harmless by 
gradually adding white pulverised marble to the solution of 
the assay substance, until the effervescence ceases, and then 
warming the whole on the sand-bath, whereby all the copper 
is perfectly precipitated as carbonate, while nickel and 
cobalt remain dissolved. It is now filtered, washed, the 
residue dissolved in nitric acid, and the solution treated, as 
already explained, with ammonia. By the addition of 
carbonate of potassa to the ammoniacal fluid, and heating, 
all the manganese precipitates, while the copper remains 
dissolved in the excess of ammonia, and can be separated 
from the manganese precipitate by filtration. The manga¬ 
nese must have been present as oxide in the original solution 
in order that the precipitation by carbonate of potassa may 
be perfect. 




350 


THE ASSAY OF COPPER. 


The assayer may convince himself whether nickel or cobalt 
is present, by slightly supersaturating a blue ammoniacal 
solution, obtained by the ordinary process of assaying, with 
hydrochloric or sulphuric acid, then precipitating the cop¬ 
per completely with iron, filtering the residual solution, con¬ 
centrating somewhat, if necessary, and now supersaturating 
with ammonia. If the fluid then remains colourless, neither 
of the two metals is present; a blue colour indicates nickel, 
a red one cobalt. 

Sometimes the normal solutions which when freshly pre¬ 
pared appear azure blue, assume a greenish hue, which 
renders the comparison difficult, if not impossible. Nitrate 
of copper produces with ammonia a pure azure blue, sul¬ 
phate of copper a lilac colour, and chloride of copper green¬ 
ish hues. Sulphuric and hydrochloric acid are therefore 
avoided as much as possible in the solution. But, never¬ 
theless, an assay fluid may sometimes, e.g. by standing some 
time in the air, or by slow filtration, become green, in 
which case the colour is destroyed by a few drops of nitric 
acid, and ammonia added anew. But sometimes also the 
greenish colour disappears, if the solution stands in a 
covered vessel in the air, or by the addition of a few drops 
of red ammonio-oxide of cobalt. 

According to Muller, also, the colour stands in the closest 
connection with the quantity of ammonia employed, and it 
therefore leads to greater accuracy in the assay, if a titrated 
solution of ammonia is used, and the volume of ammoniacal 
fluid noted, which, after neutralisation of the residual free 
acid, is used for the solution of the copper. The solution 
appears more intense when viewed with a grey background 
than with a white one. A greenish blue colouring becomes 
the more noticeable, the greater is the excess of ammonia, 
or the more ammoniacal salts are in the solution. 


2. Jacquelain’s and Von Hubert’s Colorimetric Assays. 

Heine’s method, for the reasons stated, is suitable only 
for the determination of small quantities of copper. Jac- 



THE ASSAY OF COPPER. 


351 


quelain has extended it to the examination of all cupriferous 
substances, and this process has been further perfected by 
Von Hubert. According to the latter, a solution of any 
cupriferous accurately weighed substance is prepared, mixed 
with ammonia in excess, the ammoniacal solution (assay 
solution) measured at a definite volume, and a small, like¬ 
wise measured portion of the measured solution, diluted with 
water, until its blue colour shows an equal intensity with 
the blue colour of another solution (normal solution), also 
cupriferous and ammoniacal, whose copper contents are 
known once for all. Then, from the quantity of water 
added, in order to make the two fluids equal to each other 
in the intensity of their blue colours, the amount of copper 
in the substance under examination can be determined by 
calculation. 

The normal solution is prepared by dissolving ’5 of a 
gramme of chemically pure copper in dilute nitric acid, 
adding ammonia in excess, and diluting with distilled water 
until the whole at 12° C. amounts to one litre=1000 cubic 
centimetres. The solution is filtered, and preserved in a 
flask provided with a glass stopper ground in to fit it. 

For the preparation of the assay fluid, with substances 
whose percentage of copper ranges from 1*5 to the highest 
per cent., two grammes, and with the poorer substances five 
grammes, are brought into ammoniacal solution with the 
precautions specified in Heine’s assay. This solution, with 
over five per cent, of copper, is measured at two hundred 
cubic centimetres, with two to five per cent, of copper at 
one hundred and fifty cubic centimetres, and with two per 
cent, and under, at one hundred; and also, as may be 
required, at 90, 80, 60, 50 c.c., according to the intensity 
of the fluid. Only with an extremely small quantity of 
copper is the assay fluid evaporated to a smaller volume, 
in order to be able to conduct the colorimetric test with 
accuracy. 

The comparison of the intensity of colour of the assay fluid 
with the normal fluid is accomplished in two different ways, 
according as the former, when measured at a definite volume, 
is darker or lighter than the latter. This can be seen if a 



352 


TIIE ASSAY OF COFFER. 


small arbitrary portion of each is poured into a glass tube of 
nine millimetres interior diameter, twelve centimetres in 
length, and uniform thickness, and the two tubes are held in 
parallel positions over a piece of white paper so that they rest 
firmly on it, and are inclined to it at an angle of about 45°, 
and direct light falls upon them. Shadow should not fall 
upon the tubes. 

a. The Assay Fluid is Darker than the Normal Solution .— 
By means of a pipette, five cubic centimetres of the normal 
solution are placed in a glass tube closed at the bottom and 
not graduated, and seven millimetres in interior diameter 
and twelve centimetres long. Since 1000 c. c. of the normal 
solution contain ’5 of a gramme of copper, five cubic centi¬ 
metres contain exactly *0025 and the ratio 5 : *0025 ex¬ 
presses once for all the known proportion of copper in the 
normal solution. 

Five cubic centimetres of the definitely measured assay 
fluid are now also placed in a beaker and gradually diluted 
with water till they show the same intensity of colour as the 
normal solution. In the comparison the assay fluid must be 
in a similar tube to that containing the normal solution. 
With richer proportions a greater accuracy is attained in 
this comparison, if the assay fluid is so far diluted that its 
intensity still appears as little as possible darker than that of 
the normal solution, and then water added carefully, and 
drop by drop, till its intensity is judged as little as possible 
lighter than that of the normal solution, whereupon the 
mean of the two volumes noted is taken as the correct value. 
The measuring of the diluted assay fluid is performed in glass 
tubes of nine millimetres interior diameter and fifty centi¬ 
metres in length, which from their lower closed end to the 
circular mark designated by 0, hold exactly five cubic cen¬ 
timetres, and from 0 upwards are divided into cubic cen¬ 
timetres and their tenths. 

If, for example, two grammes of the assay substance have 
been weighed out, the assay fluid measured at 200 cubic cen¬ 
timetres, and five cubic centimetres of it diluted to 8*2 cubic 
centimetres, in order to obtain an equal intensity of colour 
between the normal and assay fluid, then the percentage of 


THE ASSAY OF COFFER. 


353 


copper, x , follows from this according to the following chain 
of ratios :— 


X 

2 

6 

■5 

x 


100 per cent. 

200 c. c. assay fluid. 

8-2 c. c. diluted assay = normal solution. 
•0025 grammes of copper in normal solution. 
= 8-2 per cent, of copper. 


b. The Assay Fluid is Lighter than the Normal Solution .— 
In this case five cubic centimetres of the normal solution 
are diluted till their intensity is equal to that of the assay 
solution that has been measured at a definite volume, and for 
the comparison larger tubes of nine millimetres interior dia¬ 
meter are used. 

If, for example, two grammes of the assay substance have 
been weighed out, 150 cubic centimetres of assay fluid ob¬ 
tained from it, and to get the same intensity of colour, five 
cubic centimetres of the normal solution diluted to 8*4 cubic 
centimetres, the quantity of copper x amounts, according to 
the following chain of ratios, to 2*205 per cent.:— 


X 

2 

8-4 

5 

x = 16-8 


100 per cent. 

150 c. c. assay solution. 

5 c. c. normal solution. 
•0025 grammes of copper. 
37’5 = 2 205 per cent. 


This assay is adapted for all cupriferous substances, since 
nickel, cobalt, and manganese, which would influence the 
result unfavourably, can be removed without particular 
difficulty. It is also easy to be learned by those less 
practised in analytical operations, can be completed in a few 
hours, and is far less expensive than the dry assay. From 
two to one tenth per cent, of copper can also be deter¬ 
mined by it with accuracy. 

Heine, however, prefers his method when a small percen¬ 
tage of copper is to be determined, since by it even one 
loth of copper in the centner = *03 per cent, can be de¬ 
termined, and there is less liability to error. While in slag 
assays with nine to eighteen loth of copper in the centner, 
by Heine’s method, errors of half a loth are not to be 
avoided, variations of more than one loth occur by Yon 
Hubert’s process. The latter works with a too deeply 
coloured normal fluid, corresponding to a solution of over 

A A 






354 


THE ASSAY OF COPPER. 


fourteen loth of copper to one ounce of water, while Heine 
does not exceed four loth. The process is surer if the fluids 
are diluted and thicker layers of them compared, and thus 
the hue made artificially deeper, than if small quantities of 
stronger fluids are compared and the hue made artificially 
lighter by comparing them in thinner layers, or especially in 
tubes, where the light is dispersed and shade produced. The 
comparison in oblong glasses is therefore to be preferred to 
that in tubes. 

By a comparison of Von Hubert’s assay with that of the 
Oberhartz, it appears that, as Yon Hubert’s experiments 
themselves have shown, both give equally accurate results 
for substances not too poor in copper (i.e. containing not 
less than 5 per cent.). The Oberhartz assay allows a direct 
determination of the copper, requires less apparatus, is also 
very simple, and can be completed in a shorter time. Since 
different individuals are differently susceptible to colours, and 
the blue colour of the ammonio-oxide of copper, in conse¬ 
quence of causes yet unknown, sometimes inclines more or less 
to greenish, and thereby renders observation difficult, there¬ 
fore, for the sake of greater certainty, though not of greater 
accuracy, those assays by which a determination of the copper 
is possible by weight, should in general be preferred to the 
colorimetric methods, and this is the case with the Oberhartz 
assay down to two per cent. With smaller percentages the 
colorimetric assay must be called to our aid. It is not yet 
settled that with higher percentages of copper the principle 
of colorimetry is a correct one ; that is, that the intensity 
of the colour is directly proportional to the quantity of the 
colouring agent. 

Since ammoniacal solutions poor in copper often show a 
dash of greenish, Yon Hubert prepares a normal solution for 
such by dissolving one decigramme of copper and diluting 
to one litre of fluid. 

3. A. Muller’s Assay with the Complementary Colorimeter. 

Muller has sought to remove the uncertainties in the com¬ 
parison of colours which arise in direct inspection, by a 


pelouze’s volumetric method. 


355 


new colorimeter, which is based upon the neutralisation of 
the colour to be measured, by its complementary colour. For 
cupriferous ammoniacal fluids a more or less reddish yellow 
is suitable, according to their character. 

This process, for the detailed management of which refe¬ 
rence must be made to the publications of Muller, consists 
essentially in determining in millimetres the height of the 
column of fluid of a dilute ammoniacal solution with a known 
percentage of copper, which, when the laterally falling light 
is cut off with a complementarity coloured glass plate placed 
over the fluid, will produce the neutralisation point, i.e. white 
light. For every testing of an assay fluid instituted with the 
same glass plate, the percentage of colouring matter then fol¬ 
lows in inverse proportion to the actual height of the column 
of fluid. If the volume of the assay fluid is also measured, 
which is directly done with great accuracy in the apparatus 
itself, all the data are obtained for the calculation of the 
amount of copper in the assay substance, after the necessary 
corrections, constant for each instrument, have been taken 
into consideration. 

As the experiments of Heine, and also investigations made 
in the metallurgical laboratory at Clausthal, have demon¬ 
strated, large and small quantities of copper can be quickly 
determined with great accuracy by means of this colorimeter. 

cl. VOLUMETRIC COPPER ASSAYS. 

1. Pelouze’s Copper Assay [precipitation analysis] with 

Sulphide of Sodium. 

Pdouze's Process .—This is dependent on the decolorisation 
of an ammoniacal solution of copper by sulphide of sodium. 
The standard solution of sulphide of sodium may be made 
by dissolving four ounces of crystallised sulphide of sodium 
in a quart of water. To determine the strength of this solu¬ 
tion proceed as follows :— 

Dissolve 20 grains of pure copper in nitric acid, dilute 
the solution with water, add excess of ammonia, and make 
up the deep blue solution thus afforded to about half a 
pint, which introduce into a suitable flask, and heat to 


356 


THE ASSAY OF COFFER. 


ebullition. Whilst the contents of the flask are in process of 
boiling, pour into a burette, divided into 100 parts, 100 
measures of the solution of sulphide of sodium, and when 
the cupreous solution is boiling, gradually add the sulphide 
of sodium until the liquid in the flask becomes colourless : 
it must be kept in a constant state of ebullition. When this 
is the case; the whole of the copper is thrown down as a 
black precipitate of oxysulphide of copper (5CuS,CuO). 

The number of degrees of solution of sulphide of sodium 
required to produce this effect must be noted, and the 
numbers so used are equivalent to and represent 20 grains 
of copper. 

Suppose 186 measures or degrees had been necessary, 
then as 


20 x l 

186 : 1 :: 20 : x =-= 0-1075 

186 

so that every division or degree in the burette corresponds 
to 0T075 grain of copper; and in the assay proper the 
operator has only to multiply the number of divisions used 
by the number obtained as above, and the result will be the 
amount of copper in the quantity of ore or other material 
operated on. 

The assay of the ore is thus made:—50 grains are dis¬ 
solved in nitric acid, or in nitro-hydrochloric acid (aqua 
regia), as may be found most advantageous. When the 
solution is complete, the flask is allowed to cool, water 
added, and then considerable excess of ammonia. If the 
precipitate thus produced be very bulky, it must be sepa¬ 
rated by filtration, well washed, and the washings added to 
the filtrate ; if not, the small amount need not be sepa¬ 
rated. The solution must now be boiled, and the sulphide 
of sodium added as just described. When the blue colour 
of the solution in the flask has disappeared, the number of 
divisions is noted, and multiplied by the number obtained in 
standardising the solution as already described. The result 
is the quantity of copper in 50 grains : this multiplied by 
2 gives the percentage. 



KUNSEL’S VOLUMETRIC METHOD. 357 

Pelouze made a great number of experiments to ascertain 
how far the presence of other metals might interfere with 
the accuracy of this process, and his results assure him that 
nickel and cobalt alone have any injurious effects; and for¬ 
tunately these occur but seldom, and in small quantities, in 
copper ores and their products. 

2. C. Kunsel’s Volumetric Method for the Estimation of 
Copper and Nickel and Copper and Zinc. 

Dr. C. Kunsel has proposed the following plan of estima¬ 
ting copper volumetrically. 

With careful manipulation, the author states that the 
error, at the most, will be, in the case of copper, \ per cent, 
in the case of nickel, per cent. ; and in the case of zinc 
\ per cent. 

An ammoniacal solution containing - 1 Q - V Q - 0 th of copper 
reacts distinctly on moist, recently precipitated sulphide of 
zinc, the zinc dissolving while the copper is precipitated in 
the form of sulphide. The sulphides of zinc and nickel de¬ 
compose instantly in a hot ammoniacal solution of copper. 
A solution which contains ^Q^tli of sulphide of sodium 
reacts distinctly on an ammoniacal silver solution or a 
solution of nitro-prusside of sodium. 

Starting from these three reactions, the author proposes 
the following volumetrical methods for nickel and copper 
or copper and zinc:— 

1. Sulphide of Sodium Solution .—It being necessary to 
make use of pure sulphide of sodium, the author prepares it 
by saturating a solution of caustic soda free from carbonate, 
with sulphuretted hydrogen, and driving off* the excess of 
the gas. The solution is then diluted so that a cubic centi¬ 
metre precipitates a centigramme of copper or nickel. 

2. Standard Test: Preparation of Standard Solution of 
Sulphide of Sodium for Estimation of Copper .—The author 
dissolves a known weight of pure copper in nitric acid, 
supersaturates the solution with ammonia, dilutes it, and 
heats it to boiling. The solution of sulphide of sodium is 
then added to the hot solution of copper, stirring continually 





358 


THE ASSAY OF COPPER. 


until a drop of the mixed solution no longer colours sulphide 
of zinc brown. Sulphide of zinc for indicating the complete 
precipitation of the copper is prepared in the following 
way:—Zinc is dissolved in hydrochloric acid, the solution is 
supersaturated with ammonia, and is then boiled with a little 
sulphide of zinc to remove the lead which is always present 
in commercial zinc. The ammoniacal solution of zinc, now 
free from lead, is filtered, and decomposed with sulphide of 
sodium, a small quantity of zinc being allowed to remain in 
solution. The moist sulphide of zinc, with excess of zinc 
solution, is then spread evenly upon filter paper several 
layers thick. When the paper has absorbed most of the 
solution, the moist white layer of sulphide of zinc is ready 
for use. 

3. Test Solution for Nickel .—The strength of the solution 
for nickel is ascertained in a similar way to the preceding. 
A known weight of nickel is dissolved in acid, the solution 
is treated with excess of ammonia, diluted with water, and 
the solution of sulphide added until a drop of the mixed 
solutions colours an ammoniacal solution of silver pale 
brown, or gives a red with nitro-prusside of sodium ; i. e. 
until all the nickel is precipitated, and a slight excess of the 
sulphide is present in the mixture. But as freshly precipi¬ 
tated sulphide of nickel will colour the silver solution brown 
and redden the nitro-prusside, it is necessary to separate the 
precipitate before the solution is tested. The author there¬ 
fore filters a drop by placing it on a strip of filtering paper, 
and applies the silver solution or nitro-prusside to the moist 
spot on the opposite side of the paper. 

4. Test Solution for Zinc .—In the case of zinc the author 
recommends pure chloride of nickel to be used to indicate 
the complete precipitation. The strength of the solution of 
sulphide of sodium having been ascertained in the experiment 
with copper, it may be obtained for nickel and zinc by 
calculation. 

5. Process for Copper and Nickel —The ore or alloy 
freed from arsenic is dissolved in hydrochloric acid, with the 
addition of some nitric acid, and, when necessary, is evapo¬ 
rated to dryness, the deposit dissolved in hot water, and 


RARKES’ AND MOHR’S METHOD. 


3.59 


filtered to separate silica. Any iron may be removed from 
the mixed chlorides by the addition of ammonia. The 
solution, freed from iron, is then rendered strongly ammoni- 
acal, heated to boiling, and the standard solution of sulphide 
of sodium added (with continual shaking), until a drop of 
the mixed solutions no longer acts on sulphide of zinc, i.e. 
until all the copper is precipitated. The number of cubic 
centimetres ot the standard solution is then read off, and the 
amount of copper calculated. The addition of the standard 
solution is now continued until there is a trace of the sul¬ 
phide in excess in the mixture, which is ascertained in the 
manner before described ; the additional number of cubic 
centimetres employed will give the amount of nickel. 

6. Process for Copper and Zinc .—This may be the same 
as the foregoing process for copper and nickel, making use 
of chloride of nickel to indicate the complete precipitation 
of the zinc. 


3. Parkes’ and Mohr’s Method by Cyanide of Potassium. 

In carrying out the volumetric estimation according to 
the directions of Mr. Parkes, a solution of cyanide of 
potassium is slowly added to a blue ammoniacal solution of 
copper, when the latter gradually loses its colour, and finally 
becomes quite colourless ; upon this chemical reaction the 
estimation of copper by cyanide of potassium depends. By 
ascertaining by direct experiment the amount of cyanide of 
potassium solution required to discharge the colour in an 
ammoniacal solution containing a given weight of copper, it 
is easy by a comparative experiment to determine the amount 
of copper in a given weight of ore. 

For the preparation of the standard solution 2,000 grains 
of fused cyanide of potassium are to be dissolved in two 
quarts of water, to produce a solution of which 1,000 grains 
measure will be equal to about ten grains of metallic 
copper. The solution should be preserved in green glass 
stoppered bottles, and kept as much as possible away from 
the light; it is liable to a slow decomposition, which will 




3G0 


TIIE ASSAY OF COPPER. 


necessitate the standard being checked at intervals of one 
or two weeks. In order to standardise the solution, a 
burette, holding 1,000 grain measures, is filled to the zero 
mark, and a piece of pure electrotype copper previously 
cleaned by means of dilute nitric acid, washed and dried, 
is accurately weighed. About eight grains may be con¬ 
veniently taken; this is dissolved in a pint flask by dilute 
nitric acid, and, after the energy of the first action has 
subsided, the solution is warmed and ultimately boiled to 
expel all the nitrous acid fumes. It is diluted with cold 
water to the bulk of nearly half-a-pint, treated with 
ammonia in excess, and to the deep blue solution the 
cyanide is added from the burette until the colour is so 
nearly discharged that a faint lilac tint only remains. This 
will generally become quite bleached on standing at rest 
for a short time, so that the cyanide must not be added too 
hastily towards the end of the operation. It will be ad¬ 
visable to control the standard by a second experiment upon 
another weighed portion of copper, and to stop short of 
bleaching entirely the faint lilac tint of the solution. A 
piece of white paper folded and placed under and behind 
the flask during the decolorisation, will aid in recognising 
the proper tint of the solution. 

In applying this process to the examination of copper 
ores, a known weight of the finely-powdered sample is 
introduced into a beaker provided with a glass cover, and 
moistened with strong sulphuric acid ; strong nitric acid is 
then added, and the whole digested on a sand-bath until 
nitrous fumes are no longer given off. Should a small 
quantity of sulphur be separated in the treatment of pyrites 
ores, the small globules may be taken out, burnt, and the 
residual copper dissolved in a few drops of nitric acid and 
mixed with the remainder. Water is now to be added and 
left in contact for a short time to extract all the metallic salt 
from the insoluble residue, which need not be filtered off; 
and so, likewise, when ammonia is added in the next place, 
any peroxide of iron which may thus be precipitated is left 
in the solution, for it is apt to contain a small proportion 
of copper when first thrown down ; but this is entirely 


SCIIWAEZ’S METHOD. 


361 


removed by the cyanide of potassium later in the experi¬ 
ment. 

When the ore contains much iron it is considered desirable 
to remove the hydrated peroxide by filtration, in order to 
be enabled to determine with greater precision the last effects 
of the cyanide of potassium; and in the event of requiring 
to know the amount of iron present in the ore, the precipi¬ 
tated peroxide on the filter is re-dissolved in dilute sulphuric 
acid, reduced to the state of protoxide by metallic zinc, and 
then tested in the usual way with a standard solution of 
permanganate of potash. 

The metals which interfere with this mode of valuing 
copper ores, are silver, nickel, cobalt, and zinc. The first 
may readily be separated by adding a few drops of hydro¬ 
chloric acid to the original solution; the other metals may 
be excluded by following one of the methods pointed out 
by the author for that purpose. 

4. Schwarz’s Method with the Modification of F. Mohr. 

•G34 grammes of the assay substance are dissolved in water 
or acid, the solution placed in a flask, the excess of acid neu¬ 
tralised with carbonate of soda, a small quantity of neutral 
tartrate of potash and caustic potash or soda added, till all 
is dissolved to a deep blue fluid. If this does not take place 
at once, more tartrate of potash is added. The solution is 
warmed to 40—50° E., and pure starch- or honey-sugar, or 
pure white honey, added, with frequent shaking, whereby the 
oxide of copper is gradually reduced, and finally a fire-red 
precipitate of suboxide of copper produced, so that the fluid 
assumes a yellowish colour. With too strong boiling the pre¬ 
cipitate becomes brownish-red. The diluted fluid is filtered, 
the precipitate well washed with hot water, and together with 
the filter put into a wide-necked flask, and a suitable quantity 
of chloride of sodium, and then hydrochloric acid, added, 
whereupon the suboxide of copper dissolves to colourless sub¬ 
chloride of copper, forming an easily soluble double salt with 
the chloride of sodium. Without removing the filter, titrated 
solution of permanganate of potash is then added to the 


362 


THE ASSAY OF COFFER. 


solution from a Gay-Lussac burette, with constant stirring, 
until its rose-colour, which is destroyed by the oxidation 
of the suboxide of copper, again appears. The permanganate 
of potash solution is so titrated that 100 cubic centimetres 
of it correspond to *56 gramme of iron. The cubic centi¬ 
metres used then give the copper in per cents. 

The calculation depends upon the fact that one atom of 
suboxide of copper, Cu 2 0, takes one atom of oxygen from 
the permanganate of potash to form oxide of copper, and 
two atoms of protoxide of iron, which contain two atoms of 
iron, also take one atom of oxygen to form sesquioxide of 
iron; hence one atom of iron corresponds to one atom of 
copper, or twenty-eight of iron to 31*7 of copper, so that 
from the percentage of iron which the titrated solution of 
permanganate of potash gives, the percentage of copper may 
be calculated. 


5. E. 0. Brown’s Method by Hyposulphite of Soda. 

The process described by Mr. E. 0. Brown is particularly 
applicable to the determination of copper in gun-metal, brass, 
and other alloys which contain no large amounts of iron and 
lead. It is founded on the reactions between salts of copper 
and the neutral iodides, and on the conversion of the 
liberated iodine into hydriodic and tetrathionic acids by a 
standard solution of hyposulphite of soda. 

These reactions may be thus expressed:— 

2(CuO,A) + 2KI = Cu 2 I + I + 2(KO,A) 

I + 2(JNa0,S 2 0 2 ) = JSTal + Na0,S 4 0 5 

The completion of the second reaction is manifested by the 
bleaching effect produced upon the blue iodide of starch by 
the addition of the hyposulphite. A convenient strength 
of solution for this purpose may be made by dissolving 
1,300 grains of the crystallised salt in two quarts of water. 
The iodide of potassium must be free from iodate ; and a 
clear solution of starch employed. 

From 8 to 10 grains of the copper or alloy are dissolved 
in dilute nitric acid, and the red nitrous fumes expelled 



fleck’s modification of moiir’s method. 


363 


by boiling. The nitrate of copper is converted into acetate 
by adding carbonate of soda until a portion of copper 
remains precipitated, and then re-dissolving in acetic acid. 
The solution is diluted with water, and about GO grains of 
iodide of potassium in the form of crystals dropped into the 
flask, and allowed to dissolve. The standard solution of 
hyposulphite of soda is now poured in from a burette, until 
the greater part of the dark-coloured free iodine disappears. 
A little of the starch solution is now added to make its pre¬ 
sence more apparent, and the addition of the hyposulphite 
continued until the bleaching is completed, when the pale 
yellow colour of the subiodide of copper will alone be 
visible. The amount of copper in the ore or alloy is cal¬ 
culated from the number of divisions indicated upon the 
burette. 

Copper ores containing much iron (which interferes by 
reason of the dark red colour of the acetate) may be dis¬ 
solved in nitric acid, and treated with sulphuretted hydrogen 
to precipitate the copper, the sulphide being collected on a 
filter, washed, and re-dissolved in nitric acid to produce a 
solution suitable for testing by this process. Or the hypo¬ 
sulphite may itself be employed to furnish a precipitate of 
disulphide of copper. 

6. Fleck’s Modification of Mohr’s Method.* 

The proposal to take the action of solution of cyanide of 
potassium on ammoniacal solution of copper, as the founda¬ 
tion of a method for estimating copper, is due to Carl 
Mohr.f 

The azure blue colour disappears, Cu 2 Cy,NII 4 Cy and 
KO are formed, while 1 eq. of cyanogen is separated, 
which acting on the free ammonia, gives urea, oxalate 
of urea, cyanide of ammonium, and formiate of ammonia 
(LiebigJ). 

* This process is given by Fresenius, condensed from Polyteclm. Centralbl. 
1859, 1313. 

t Annal. d. Chem. u. Pliarm. 94, 198; Fr. Mohr’s Lehrbuch der Titrier- 
niethode, 2, 91. 

| Annal. d. Chem. u. Pliarm. 95, 118. 


364 


TITE ASSAY OF COPPER. 


The decomposition is not always the same : the quantity 
and degree of concentration of the ammonia has a marked 
influence on it, from which it appears that neutral am¬ 
monia salts also affect the results. 

Fleck proposes the following modification :— 

Instead of caustic ammonia, use a solution of sesquicar- 
bonate of ammonia (1 in 10), warm the mixture to about 
60°, and in order to render the end reaction plainer, add 2 
drops of solution of ferrocyanide of potassium (1 in 20); the 
blue colour of the solution is not altered by this addition, 
nor is its clearness affected. The value of the cyanide of 
potassium solution is first determined, by means of copper 
solution of known strength, and it is then employed on the 
copper solution to be examined. On dropping the cyanide 
of potassium into the blue solution warmed to 60°, the odour 
of cyanogen is plainly perceptible, and the colour gradually 
disappears. As soon as the ammoniacal double salt of 
copper is destroyed, the solution becomes red from the 
formation of ferrocyanide of copper, without any precipitate 
appearing, and with the addition of a final drop of cyanide 
of potassium this red colour in its turn vanishes, so that the 
fluid now appears quite colourless. 

The method thus modified yields, it is true, better, but 
still only approximate results.* Where such are good 
enough, the method is certainly convenient. 


7. Fleitmanjn’s Method. 

Mr. Sutton gives the following description :— 

The metallic solution, free from nitric acid, bismuth, or 
lead, is precipitated with zinc ; the copper collected, washed, 
and dissolved in a mixture of perchloride of iron and 
hydrochloric acid; a little carbonate of soda may be added 
to expel the atmospheric air. The reaction is— 

Cu + Fe 2 Cl 3 =CuCl+2FeCl. 


* In six experiments, in which he had purposely added different quantities 
of carbonate of ammonia, Fleck used for 100 c. c. copper solution, in the 
minimum 15-2, in the maximum 1575, in the mean 15*46 c. c. cyanide of 
potassium solution. 


LEVOL’S AND OTHERS’ COPPER ASSAYS. 565 

1 eq. of copper, therefore, produces 2 eq. protochloride of 
iron. When the copper is all dissolved, the solution is 
diluted and titrated with permanganate ; 5G iron represent 
31*7 copper. 

If the original solution contains nitric acid, bismuth, or 
lead, the decomposition by zinc must take place in ammoni- 
acal solution, from which the precipitates of either of the 
above metals have been removed by filtration ; the zinc 
must be finely divided and the mixture warmed; the cop¬ 
per is all precipitated when the colour of the solution has 
disappeared. It is washed first with hot water, then with 
weak hydrochloric or sulphuric acid and water, to remove 
the zinc; again with water, and then dissolved in the acid 
and perchloride of iron as before. 

e. OTHER COPPER ASSAYS, BY LEVOL, BYER AND ROBERT, 

RIVOT, AND WOLCOTT GIBBS. 

1. Levol treats a solution of ammonio-oxide of copper, 
with exclusion of air, with a weighed strip of copper, by 
which the oxide of copper is reduced to suboxide. From 
the loss which the strip of copper suffers, the quantity 
of copper in the solution can be calculated. This assay is 
indeed accurate, if no other substances are present which 
oxidise copper, but it requires several days’ time, and the 
copper is determined by a difference, which is always more 
uncertain than a direct determination. 

A similar assay, in which, however, instead of an ammo- 
niacal solution, a hydrochloric acid solution is used, has been 
given by Bunge. 

2. Bobert and Byer precipitate the copper from its 
solution, by a simple galvanic apparatus, on a weighed 
plate of copper, whose increase in weight then gives the 
quantity of copper in the assay. The operation lasts ten to 
twelve hours, and no other similarly precipitable metals 
should be present. 

3. Bivot precipitates the suboxide of copper from its 
solution as sulphocyanide of copper Cu 2 Cy 2 S, and from the 
weight of this salt calculates the amount of copper directly, 


366 


TIIE ASSAY OF COFFER. 


or after it has been converted into Cu 2 S by igniting with 
sulphur in a covered porcelain crucible at a red heat. 

This method is indeed accurate, and generally practicable, 
but it requires a complete acquaintance with the analytical 
operations and the observance of a mass of small precautions, 
so that it does not differ from an analytical process. 

Professor Chapman, of Toronto, gives the following direc¬ 
tions for the detection of minute traces of cppper in iron 
pyrites and other bodies:— 

Although an exceedingly small percentage of copper may 
be detected in blowpipe experiments by the reducing process 
as well as by the azure blue coloration of the flame when 
the test-matter is moistened with chlorhydric acid, these 
methods fail in certain extreme cases to give satisfactory 
results. It often happens that veins of iron pyrites lead at 
greater depths to copper pyrites. In this case, according to 
the experience of the writer, the iron pyrites will almost 
invariably hold minute traces of copper. Hence the de¬ 
sirability, on exploring expeditions more especially, of some 
ready test by which, without the necessity of employing 
acids or other bulky and difficultly portable reagents, these 
traces of copper may be detected.* The following simple 
method will be found to answer the purpose:—The test 
substance, in powder, must first be roasted on charcoal, or, 
better, on a fragment of porcelain,f in order to drive off 
the sulphur. A small portion of the roasted ore is then to 
be fused on platinum wire with phosphor-salt; and some 
bisulphate of potash is to be added to the glass (without 
this being removed from the wire) in two or three suc- 

* In blowpipe practice—as far, at least, as this is possible—the operator 
should make it an essential aim to render himself independent of the use of 
mineral acids and other liquid and inconvenient reagents of a similar character. 
If these reagents cannot be dispensed with altogether, their use, by improved 
processes, may be greatly limited. 

t In the roasting of metallic sulphides, &c., the writer has employed, for 
some years, small fragments of Berlin or Meissen porcelain, such as result 
from the breakage of crucibles and other vessels of that material. The test 
substance is crushed to powder, moistened slightly, and spread over the 
surface of the porcelain ; and when the operation is finished, the powder is 
easily scraped off by the point of a knife-blade or small steel spatula. In 
roasting operations, rarely more than a dull red heat is required ; but these 
porcelain fragments may be rendered white-hot, if such be necessary, without 
risk of fracture .—Canadian Journal, September 1860. 


be. gibbs’s peocess. 


367 


cessive portions, or until the glass becomes more or less 
saturated. This effected, the bead is to be shaken off the 
platinum loop into a small capsule, and treated with boiling 
water, by which either the whole or the greater part will 
be dissolved ; and the solution is finally to be tested with a 
small fragment of ferrocyanide of potassium ( 4 yellow prus- 
siate ’). If copper be present in more than traces, this re¬ 
agent, it is well known, will produce a deep red precipitate. 
If the-copper be present in smaller quantity—that is, in 
exceedingly minute traces—the precipitate will be brown or 
brownish-black; and if copper be entirely absent, the pre¬ 
cipitate will be blue or green—assuming, of course, that 
iron pyrites or some other ferruginous substance is operated 
upon. In this experiment the preliminary fusion with 
phosphor-salt greatly facilitates the after solution of the sub¬ 
stance in bisulphate of potash. In some instances, indeed, 
no solution takes place if this preliminary treatment with 
phosphor-salt be omitted. 

Dr. Wolcott Gibbs recommends the electrolytic pre¬ 
cipitation of copper and nickel as a method of analysis. He 
says: — 

The precipitation of copper by zinc, in a platinum vessel, 
with the precautions recommended by Fresenius, leaves 
nothing to be desired, so far as accuracy, ease, and rapidity 
of execution are concerned. The method labours, however, 
under a single disadvantage—the introduction of zinc renders 
it difficult, or at least inconvenient, to determine with accu¬ 
racy other elements which may be present with the copper. 
It has occurred to me that this difficulty might be overcome, 
the principle of the method being still retained, by pre¬ 
cipitating the copper by electrolysis with a separate rheo- 
motor. The following numerical results, which are due to 
Mr. E. Y. M'Candless, will satisfactorily show the advantages 
of the method for the particular cases in which it is desirable 
to employ it. The copper was in each case in the form of 
sulphate : the deposition took place in a small platinum 
capsule, which was made to form the negative electrode of 
a Bunsen’s battery of one or two cells, in rather feeble 
action. The positive electrode consisted of a stout platinum 


368 


TIIE ASSAY OF COFFER. 


wire, plunged into the surface of the solution of copper at 
its centre. The following table gives the results obtained in 
the analysis of pure sulphate of copper :— 


Number 

Salt taken 

Copper found 

Percentage 

1 

1-2375 

0 3145 

25-41 

2 

0-4235 

01075 

25-38 

3 

1-0640 

0-2705 

25-42 

4 

1-3580 

0-3440 

25-33 

5 

0-5665 

01450 

25-59 

G 

0-4735 

0-1205 

25-48 


In seven determinations of copper in the alloy of copper 
and nickel employed by the Government for small coins the 
following results were obtained :— 

o 


Number 

Weight of Alloy 

Copper 

Percentage 

1 

0-4160 

0-3640 

87-50 

2 

0-6180 

0-5410 

87-54 

3 

0-4600 

0-4090 

88-91 

4 

0-5120 

04481 

87-51 

5 

0-4220 

0-3693 

87-51 

6 

0-2525 

0-2225 

88-] 1 

7 

0-3705 

0-3255 

87-85 


The percentage of copper required by the formula CuO, 
S0 3 4- 5HO is 25*42, while the Government standard alloy 
of nickel and copper contains 87*50 per cent, of copper. 
The time required for precipitation varied from one to three 
hours, the separation of the last traces of copper being in 
each case determined by testing a drop of the liquid upon 
a porcelain plate with sulphuretted hydrogen water. The 
copper after precipitation was washed with distilled water, 
dried in vacuo over sulphuric acid, and weighed with the 
platinum vessel. The only precaution necessary is to regu¬ 
late the strength of the current so that the copper may be 
precipitated as a compact and bright metallic coating, and 
to dry as quickly as possible. When the copper is thrown 
down in a spongy condition, it not only oxidises rapidly, but 
it is impossible to wash out the last traces of foreign matter 
contained in the solution. This is well shown by No. 3 and 
No. 4 of the second series, in both of which cases the copper 
was precipitated too rapidly. The solution from which the 





















BLOWPIPE REACTIONS OF COPPER. 


369 


copper has been deposited contains the other elements 
present in the original substance. It may be easily poured 
off without loss, and the washings added. 

It appears at least probable that nickel may be determined 
by electrolysis in the same manner as copper, the solution 
employed being the ammoniacal sulphate with excess of free 
ammonia. Mr. M’Candless obtained in two determinations 
in a commercial sample 91*36 and 91*60 per cent, of nickel. 
In both cases the nickel was thrown down completely as a 
bright, coherent, metallic coating upon the platinum. 

BLOWPIPE REACTIONS OF COPPER. 

Minerals of CoprEK. 

Sulphide of Copper. — Alone , on charcoal, gives off sulphu¬ 
rous acid, fusing readily in the outer flame. In the inner 
flame it is covered with a crust, and does not fuse. 

In the open tube sulphurous acid is disengaged, but no 
sublimate is produced. The residue, treated with soda and 
borax, gives a button of copper. 

Argentiferous Sulphide of Copper. — Alone , fuses easily, 
giving off sulphurous acid. Cupelled with lead, on bone-asli, 
it leaves a large bead of silver, and the cupel appears a 
blackish green. 

Sulphide of Antimony and Copper, Bournonite. — Alone , 
in the open tube, gives off the antimonial smoke, with an 
odour of sulphurous acid. A slip of Brazil-wood paper, on 
being placed within the tube, is bleached. 

On charcoal , a deposit of antimony, but no trace of 
lead. The bead diminishes in size, becoming grey, and 
semi-malleable. Fused with soda, it gives a grain of 
copper. 

Copper Pyrites, Sulphide of Iron and Copper. — Alone , on 
being heated, blackens, becomes red by cooling, and fuses 
more easily than the sulphide of copper, finally giving 
a bead attractable by the magnet. This bead is brittle, 
and reddish-grey in the fracture. If after a long exposure 
to the oxidising flame it be treated with a small quantity of 
borax, a regulus of copper is obtained. 


370 


THE ASSAY OF COFFER. 


In the open tube, much sulphurous acid is given off. 

With Soda, reduced iron and globules of copper are 
obtained, provided the ore has been sufficiently roasted. 

Sulphide of Tin and Copper, Tin Pyrites. —Beforet he 
blowpipe it becomes, by roasting, covered with a snow-white 
powder, which is oxide of tin. The white powder also 
encircles the globule to the extent of about two lines. 

In the open tube, sulphurous acid is given off. 

Needle-ore, Aikenite.— Alone , it fuses, giving off vapour, 
which coats the charcoal snow-white, slightly yellowish on 
the interior edge, finally giving a metallic bead resembling 
bismuth. 

In the open tube it gives off a white smoke, one part of 
which is fusible, and the other volatile. The first part is 
converted by fusion into limpid drops, which become white 
by cooling; there is also an odour of sulphurous acid. 
Treated by fluxes, the resulting bead of bismuth gives the 
reaction of copper. After a long blast, a grain of copper 
may be obtained, which by cupellation with lead gives traces 
of silver. A fusible white smoke, at the commence¬ 
ment of the operation, indicates the presence of tellurium. 

Chloride of Copper. — Alone , colours the flame blue, 
with greenish edges. A red pulverulent deposit forms on 
the charcoal around the assay; the fused matter reduces, 
giving a grain of copper, surrounded by slag. 

With fluxes, the chloride behaves as the oxide. 

Carbonate of Copper.— Alone, in the matrass, gives water, 
and blackens. 

On charcoal it fuses, and behaves like oxide of copper. 

Arseniate of Copper behaves with fluxes in the same 
manner as the oxide of copper, but exhales a strong odour 
of arsenic, and gives, when reduced with soda, a white 
and brittle bead. 

Oxide of Copper. — Alone , in the oxidising flame, it is fused 
into a black bead, which is reduced on charcoal. In the 
reducing flame, at a temperature which does not suffice to 
fuse copper, the oxide is reduced, and shines with the lustre 
characteristic of metallic copper; but as soon as the blast 
ceases the metal re-oxidises, and becomes black or brown. 



BLOWPIPE REACTIONS OF COPPER. 


371 


Exposed to a stronger heat, it gives a bead of metallic copper 
on fusion. 

With borax , oxide of copper readily fuses in the oxidising 
flame, forming a beautiful green glass, which loses its colour 
in the reducing flame, but which on cooling becomes 
cinnabar-red and opaque. If the oxide of copper be impure, 
the glass is generally deep brown, and only becomes opaque 
in an intermittent flame. 

With microcosmic salt it fuses, attended with the same 
phenomena as with borax. If the quantity of copper be 
small, the glass occasionally becomes transparent and ruby- 
coloured in the reducing flame ; this change takes place 
at the instant of solidification. Commonly the glass becomes 
red and opaque, similar in appearance to an enamel. 

When the quantity of the copper is so small that the 
character of the red oxide cannot be made evident in the 
reducing flame, a small quantity of tin must be added, and 
the flame kept up only for an instant. The glass, previously 
colourless, becomes red and opaque by cooling. If the blast 
be kept up too long, the colour is destroyed, owing to the 
reduction of the popper. 

With soda , on the platinum wire, a beautiful green glass 
is formed, which becomes opaque and colourless on cooling. 
On charcoal it is absorbed, and the oxide reduced. The 
blowpipe is capable of detecting a smaller quantity of 
copper than any other test; especially when it is not in com¬ 
bination with other metals, which by their reduction would 
disguise its presence. In the latter case we must use borax 
and tin. When copper and iron are associated together, 
a single assay separates them into distinct particles ; the 
one may be told by colour, and the other by being attracted 
by the magnet. 

It is difficult, by borax or microcosmic salt, to determine 
this copper in slags as protoxide or suboxide, on account 
of the small quantity generally present; and, more¬ 
over, the other ingredients, which are chiefly silicates of 
different earths and difficultly reducible metallic oxides, 
destroy the reaction of oxide of copper. For this reason, 
instead of employing the reduction process, the slags must 


372 


THE ASSAY OF COFFER. 


be treated with soda on charcoal. If by this method, also, 
copper should not be detected, a greater quantity, about 
100 milligrammes, must be reduced with its own quantity 
of soda, half of borax, and 30 to 50 milligrammes proof 
lead, and the lead, united to a globule, treated'with boracic 
acid till all is dissolved, or the copper, is concentrated. If 
the slag contains a trace of copper, this becomes reduced, 
and combines with the lead, and, in the first case, colours 
the boracic acid red, green, or blue. If the copper present 
is very minute, the tinge is seen on those parts only where 
the latter part of the lead containing copper was dissolved. 

A small quantity of copper contained in a substance can 
often be detected, if not in combination with sulphuric acid, 
by one or two drops of hydrochloric acid. It is only 
necessary to moisten the substance with this acid, and heat 
it in the forceps, in the azure of the blue flame, when, by this 
means, the outer flame is coloured greenish-blue, and often 
reddish-blue, by the chloride of copper formed. 


CHAPTER X* 


ASSAY OP LEAD. 

All minerals and substances containing lead may, for the 
purposes of the asssayer by the dry way, be divided into 
four classes :— 

Class I. comprises sulphides, antimonial or otherwise 
(galena, &c.). 

Class 1L includes all plumbiferous substances containing 
neither sulphur nor arsenic, or mere traces only of these 
elements (litharge, minium, carbonate of lead, native and 
artificial, lead fume, cupel bottoms, furnace hearths, lead 
slag, &c.). 

Class 111. comprises all substances into whose composi¬ 
tion either sulphuric, arsenic, chromic, or phosphoric acid, 
or a mixture of either, enters (pyromorphite, wolframite, 
&c.). 

Class IV. Alloys of lead. 

CLASS I. 

Before describing the different modes of assaying sub¬ 
stances of this class, it will be as well to pass in review the 
action of various reagents on sulphides of lead, in order 
that the rationale of the assay of those ores may be better 
appreciated. 

Action of Oxygen. —If galena be roasted at a very gentle 
temperature, care being taken to avoid fusion, it will be con¬ 
verted into a mixture of oxide of lead and sulphate of lead, 
with evolution of sulphurous acid, thus :— 

2 (PbS) + 70=PbO + Pb0,S0 3 + S0 2 . 

Action of Metallic Iron. —This metal completely and readily 



374 


THE ASSAY OF LEAD. 


decomposes sulphide of lead, giving metallic lead in a pure 
state, thus :— 

PbS + Fe=Pb + FeS. 

On the one side we have sulphide of lead and metallic iron, 
on the other metallic lead and sulphide of iron. 

The Alkalies and Alkaline Carbonates decompose sulphide 
of lead, but only partially ; pure lead is separated, and at 
the same time a very fusible grey slag is formed, which con¬ 
tains an alkaline sulphate and a compound of sulphide.of 
lead and an alkaline sulphide. A certain proportion of the 
alkali is reduced by the sulphur, which is converted into 
sulphuric acid, so that no oxide of lead is produced. This 
reaction may be thus expressed :— 

7 (PbS) + 4 (KO) = 4Pb + K0,S0 3 4- 3(PbS,KS). 

Nitrate of Potash completely decomposes sulphide of lead, 
with the reduction of metallic lead and formation of sulphate 
of potash and sulphurous acid, thus :— 

2(PbS) + K0,N0 5 =2Pb + K0,S0 3 + S0 2 + N. 

If the nitre be in excess, the lead will be oxidised in pro¬ 
portion to the excess present, and if there be a sufficiency 
added, no metallic lead at all will be produced. 

Argol. —The presence of carbonaceous matter much 
favours the decomposition of galena, by determining the 
reduction of a larger quantity of potassium to the metallic 
state, and thereby the formation of a larger quantity of 
alkaline sulphide. With 4 parts of argol to 1 part of 
sulphide, 80 parts of lead are reduced. If the reaction were 
complete, the decomposition would be as follows :— 

PbS + KO + C = Pb + KS + CO. 

For the reactions of oxide of lead (litharge) and the sul¬ 
phate of lead on sulphide of lead, see pages 179 and 181. 

From the reactions above given, it will be seen that there 
are many substances capable of completely reducing the lead 
from its sulphide, and yet few can be used safely with any 
advantage, as so to use them would imply a knowledge of 
how much sulphur and lead were in the ore to be assayed, 




FUSION" WITH CARBONATE OF POTASH. 375 

in order to tell the precise quantity of either of the reagents 
required ; for it is evident that if either more or less of some 
were added, a faulty result would be the consequence: so 
that some systematic mode of assay, which may be suitable 
for all classes of galena, whether mixed with other sulphides 
or with gangue, must be contrived. To facilitate this we 
now proceed to give an outline of the processes generally 
adopted in the assay of lead ores by various persons. 

1. FUSION WITH CARBONATE OF POTASH. 

This plan is used at the Oberhartz, and described by Kerl 
as follows :— 

One centner of the very finely pulverised assay substance 
is weighed out, mixed with three to four times its weight 
of pure, dry, and finely pulverised carbonate of potash, 
and covered over, in a small clay crucible (fig. 58) with 
a layer of decrepitated chloride of sodium about one-fourth 
of an inch thick. The assays thus prepared are placed 
in the thoroughly heated muffle of a large assay furnace 
(figs. 21, 22) having a strong draught. They remain in the 
highest temperature of the furnace, with the mouth of the 
muffle closed with glowing coals, till they have come into 
perfect fusion (about twenty to thirty minutes). The draught 
opening is then closed, and at the same time the muffle opened, 
until the temperature has fallen so far that the crucibles 
appear brownish-red, and the vapours above them have 
greatly diminished, or have disappeared. At this heat the 
crucibles, whose contents must, however, always remain in 
perfect fusion, are maintained, according to the fusibility 
and composition of the assay sample, and the draught of the 
furnace for a longer or shorter time (ten to twenty-five, 
generally ten minutes). This period during which the heat 
is allowed to remain low, is called the cooling of the assay. 

The furnace is now again brought back to its first tem¬ 
perature, by completely opening the draught and closing the 
muffle. Ten to fifteen minutes of this last heating are in 
most cases sufficient. Only poor ores, &c., which contain 
also a pretty large quantity of arsenic, or of the sulphides of 



376 


TIIE ASSAY OF LEAD. 


iron, zinc, and copper, are allowed to continue hot five to 
ten minutes longer. 

If one has many assays to make, it will be found advanta¬ 
geous to mix those which contain larger quantities of foreign 
sulphides, or, by reason of their earthy contents, are diffi¬ 
cultly fusible, with more or less borax , or, instead of this, to 
place them in the back and hotter part of the mu file, while 
those that are very rich in lead and easily fusible, are 
placed in front, since the latter will be hot enough here, and 
more easily reached by the air than those deeper in the 
muffle. 

The crucibles, when cold, are broken, the lead buttons 
obtained are freed from all adhering slag or substance of the 
crucible, and if the assay were otherwise successful, their 
weight determined. The assays should not be too rapidly 
cooled, because the slag is thus easily cracked, and the still 
half-fluid button lying below is apt to be broken into several 
pieces. 

In a successful assay, the lead melted together to a but¬ 
ton, deports itself under the hammer and knife like pure 
lead, and possesses also its colour. If the slag shows, upon 
its surface of separation from the metallic button, lead grey 
spots with metallic lustre, it will generally also be found that 
a thin layer of not completely decomposed glistening sulphide 
or subsulphide of lead has at the same time deposited itself 
upon the button. This layer, if the above appearance pre¬ 
sents itself in a high degree, can be rubbed off or removed in 
fine scales. The lead button itself then shows upon its sur¬ 
face a high metallic lustre, which does not have the colour 
of pure lead, but a darker and blackish hue. Assays of this 
kind are to be rejected; they have not been allowed to 
remain cool long enough, or they have in the process 
become too cold ; they give the amount of lead too low, and 
often very considerably so. In assays, which have stood 
too long in the furnace in the last fusing heat, a very bright 
button of lead is also found ; but here the layer of undecom¬ 
posed sulphide of lead is wanting, as also the glistening 
spots on the surface of the slag surrounding the button. If 
the influence of the heat and air continues too long, then 


FUSION WITH CARBONATE OF POTASII. 


377 


besides a loss through volatilisation of the lead, a slasfffino* 

' DO O 

of the oxide of lead may take place. A button that is 
brittle, laminated, and brilliantly white in the fracture, 
indicates an insufficiency of flux, or the presence of antimony 
and arsenic. In successful assays the lead button generally 
has a bluish appearance which, although not dull, is at the 
same time not strongly brilliant. The slag must be com¬ 
pletely homogeneous, and must have settled down uniformly 
towards the bottom of the crucible, so that it does not stick 
in a thick layer to the upper part of the sides of the crucible. 
It shows by this that it has been in proper fusion. It must 
have covered over the button in a thick layer (about one- 
fourth of an inch thick). The chloride of sodium covering, 
or a more or less colourless slag that is formed, containing 
chloride of sodium and carbonate of potash, overlies in a 
still thicker layer the true dark-coloured slag containing the 
foreign metallic oxides. A porous slag containing metallic 
globules indicates a small quantity of flux or too low a tem¬ 
perature ; a brilliant vitreous slag, too high a temperature 
and a slagging of lead. An assay and its duplicate, must, 
moreover, give equal results. 

Lead matt and lead fume are smelted, with the addition of 
borax and coal-dust, with carbonate of potassa, and with the 
first the heat is allowed to last somewhat longer (perhaps 
to three-quarters of an hour) than with ores. The car¬ 
bonate of potassa assay gives for lead matt, with its not 
inconsiderable lead contents (thirty per cent, and over) 
pretty satisfactory results. 

The theory of this lead assay appears from the following. 

If perfectly pure galena is intimately mixed with three or 
four times its weight of good dry carbonate of potash, 
placed in a clay retort, and this so arranged in the muffle 
of the assay furnace that its neck projects from the mouth 
of the muffle, while in the opening of the neck a glass tube 
is closely fitted, which goes into a receiver, from which it is 
further prolonged in a second tube, it will be observed that 
at first only a little water collects in the receiver, proceeding 
from the small quantity of moisture always present in the 
carbonate of potash. Later, with an incipient red heat in 


378 


TIIE ASSAY OF LEAH. 


the retort, a gas is disengaged, which upon closer investiga¬ 
tion proves to be pure carbonic acid gas, i.e. free from sul¬ 
phurous acid (means of proof:—absence of odour ; con¬ 
ducting of the gas through a solution of manganate of 
potash, reddened by sulphuric acid; through lime and 
baryta water, and through a solution of caustic potash, and 
further examination of the solution of salts obtained). The 
disengagement of gas becomes more active with a stronger 
red heat, without yielding gases of different composition, but 
ceases again after a while. In order to obtain assurance of 
a complete decomposition, the retort may be kept for an 
hour at a very strong red heat. After the cooling and 
breaking of the retort, some pure oxide and carbonate of 
lead is found deposited in the neck of it, then a pure lead 
button upon the bottom, and over this a brown slag, free 
from little globules of lead. It consists in by far the great¬ 
est part of sulphide of potassium and still undecomposed 
carbonate of potash, but also in small part of silicate of 
potash derived from the silica of the retort. If this slag 
is treated with water till nothing further will dissolve, the 
substances named can be easily shown to exist in the solu¬ 
tion. The solution is colourless, and when supersaturated 
with acids disengages sulphuretted hydrogen, but throws 
down no sulphur. In the treatment of the slag with water, 
sulphide of lead remains behind in black flocks, even the 
exterior character of which shows that it is not undecomposed 
galena, but sulphide of lead separated from a chemical 
combination. 

If the brown slag from the retort is placed in a small 
uncovered crucible and brought back into the hot muffle of 
the assay furnace and melted, then after some time, whether 
the slag was covered with chloride of sodium or not, a button 
of lead again separates at the bottom of the crucible, and 
the brown slag now shows itself decolorised. If the cru¬ 
cible is removed from the furnace too soon, only the upper 
layer of slag is decolorised, and that lying below is still com¬ 
pletely unchanged. The decolorised slag consists of car¬ 
bonate and sulphate of potash, and no longer contains any 
trace of sulphide of potassium. 


FUSION WITH CARBONATE OF POTASH. 


379 


In the above described lead assay, the process in the strong 
preliminary heat proceeds as in the retort, i.e. the potash 
of the carbonate of potash is reduced to potassium, while it 
yields its oxygen to the sulphur of the galena and with it 
forms sulphuric acid ; the liberated potassium takes up sul¬ 
phur from another portion of galena, forming sulphide of 
potassium. The galena would now in this double way soon 
lose all its sulphur, it a combination—a sulphur salt—of 
sulphide of potassium with sulphide of lead did not form, 
which resists all further action of the carbonate of potash 
[4 (K0,C0 2 ) + TPbS=4Pb + 3 (KS,PbS) + K0,S0 3 + 4 C0 2 ]. 
The carbonic acid of the thus decomposed carbonate of 
potash escapes together with that set free by the sulphuric 
acid formed, and causes a puffing up of the mass, by which 
globules of lead already separated are raised up with it, 
and may perhaps remain with some of the slag sticking to 
the upper crucible walls. They would here oxidise and 
produce yellow spots. The covering of chloride of sodium 
is designed to guard against loss of lead in this and similiar 
ways. It serves in a certain manner to rinse down the sides 
of the crucible. 

The atmospheric oxygen, in the open crucible, is not 
entirely excluded by the covering of chloride of sodium. In 
the cooling of the assay, it oxidises the sulphur salt con¬ 
tained in the upper part of the slag, forming sulphate of 
potash and a portion of sulphate of lead. The latter, during 
the last high heat, decomposes the sulphide of lead still 
remaining in the slag, in such a way as to produce metallic 
lead. (PbS + PbO,SO s = 2Pb 2S0 2 .) The reduced par¬ 
ticles of lead separate well from the slag thus rendered 
thinly fluid. Matts must be allowed to cool longer than 
ores. 

The carbonate of potash assay presupposes in general 
great practice, and close attention on the part of the assayer; 
and moreover, if one wishes to find the correct value at 
once, without fruitless preliminary examinations, and with¬ 
out the necessity of repeating the assay, a general knowledge 
of the constituents of the assay sample, so far, for example, 
as this can be obtained by the aid of mineralogy, is necessary. 


380 


TI1E ASSAY OF LEAD 


The assay after this method, which requires but little pre¬ 
paration, can only be conducted in the muffle furnace, but 
then in pretty large number (as many as fifty at once). For 
its success it is indispensably necessary that the cooling 
of the assay be undertaken and stopped again at the right 
time and in the proper degree. If it is allowed to cool 
too long, too much sulphate of lead is formed in proportion 
to the sulphide of lead still present in the slag, and in the 
last heating up, by the action of the two upon each other, 
easily scorifiable oxide of lead is produced. (PbS 4- 3PbO, 
S0 3 = 4Pb0 + 4S0 2 .) If the cooling is too soon interrupted, 
only a small part of the sulphide of lead in the sulphur salt 
is oxidised, and by the action of the oxidised portion upon 
the sulphide of lead subsulphide of lead is produced, which 
either remains in the slag or settles upon the lead button. 
(2 PbS + Pb0,S0 3 = Pb. 2 S + 2Pb + 2S0 2 .) Experience gives 
the only means at hand to guide us here, but leaves us easily 
in the lurch, so that the result of the assay becomes more 
doubtful than in some of the methods hereafter described. 

With substances containing antimony this assay deserves 
the preference over the others, since most of the antimony 
remains in the slag in the state of sulphide and oxide. An 
addition of saltpetre works advantageously. Arsenic and 
sulphide of arsenic mostly go off in fumes during the smelt¬ 
ing, but nevertheless always cause the formation of a brittle 
metallic button. Sulphide of copper remains in great part 
in the slag, but a part of the copper is desulphurised and 
goes into the lead. If the quantity of copper present is 
very considerable, the button of metal may be considered as 
black copper, and refined, and the loss thereby occurring, 
reckoned as lead. 

Proto-sulphide of iron , which occurs, for example, in lead 
matt, is decomposed by carbonate of potash, forming me¬ 
tallic iron, which desulphurises the galena. Iron pyrites , 
on the other hand, occasions the forming of a large quantity 
of sulphide of potassium, and in consequence of this, of a 
sulphur salt. 

It follows, therefore, from the above, that ores, which 


FUSION WITH CARBONATE OF POTASH. 


3S1 


contain much foreign sulphides, are not suited to this method 
of assaying, since they cause the production of a large 
amount of sulphide of potassium, which always retains 
sulphide of lead. By an addition of saltpetre to the car¬ 
bonate of potash, these sulphides may, indeed, be partially 
decomposed : only an oxidation of the lead is apt to be pro¬ 
duced, as well as a mechanical loss by the violent action of 
the saltpetre. 

Bredberg has, in his comparative investigations of the 
different methods of assaying lead, pronounced the smelting 
of the raw ore with carbonate of potash and chloride of 
sodium, to be the most inapplicable of all. He cannot, how¬ 
ever, have understood the theory of this method, since he 
melted his assays in the crucible furnace, and, therefore, 
without access of air, and that in his investigations he must, 
therefore, have found the quantity of lead much too small, is 
perfectly evident from the above. Thus his opinion in relation 
to this method must have proved erroneous, and this may be 
mentioned here for the reason that many a verdict against 
this method of assaving has originated in the same or a 
similar mistake. 

From pure galena, by the carbonate of potash assay, 
eighty per cent, of lead at most can be obtained. Calcined 
carbonate of soda is inferior to carbonate of potash as a 
desulphurising agent, and always yields a few per cent, less 
lead than the latter. According to Phillips, seventy-five 
to seventy-seven per cent, of lead are obtained from galena 
with carbonate of soda. With cyanide of potassium, under 
certain circumstances, the same result can be obtained as 
with carbonate of potash, and it does not require so high 
nor so long continued a temperature; still it offers no real 
advantage over carbonate of potash. An addition of thirty 
to thirty-five per cent, of saltpetre to an assay, with which 
ten parts of carbonate of soda are used, promotes, indeed, 
the desulphurising of the lead, but also increases the loss of 
lead. 

At the Oberhartz smelting-house, the lead button is 
weighed out to pounds, and a difference of five pounds is 


382 


THE ASSAY OF LEAD. 


allowed between different assayers. It is also a custom, 
though not a correct one, to allow as many pounds difference 
as there are tens of pounds in the weight of the lead button 
obtained. Thus, with a lead contents of thirty and seventy 
pounds, the difference in the separate assays might amount 
to three and seven pounds respectively. 

2. FUSION WITH BLACK FLUX. 

A modification of the preceding method of assaying, 
which is sometimes employed, consists in using, instead of 
the carbonate of potash, an equal quantity of black flux, or 
indeed of argol, or in mixing a few per cent, of powdered 
charcoal or flour with the carbonate of potash, or in re¬ 
placing it in part by argol. Too great an addition of carbon 
diminishes the fusibility of the mass, and hinders the flowing 
together of the separated particles of lead. By using argol 
the operation lasts longer, because the mass remains pasty 
until most of the tartaric acid has been decomposed : but a 
greater product of lead is obtained. The chemical reaction 
during the operation is thereby modified so that the carbon 
of the black flux exerts an influence upon the potassa, and 
partially reduces it to potassium ; the potassium, thus set free, 
works now as before upon the galena. The latter is thus 
without the influence of the air more completely decomposed 
than by carbonate of potash alone, and the smelting is, 
therefore, conducted in covered crucibles (fig. 58) in the 
wind furnace. But since there also sulphide of potassium 
is formed, and this dissolves sulphide of lead, it is more 
advisable, for the completest possible separation of the 
lead, to perform the smelting in open crucibles in the 
muffle, in order to allow the atmospheric oxygen to work 
at the same time on the assay. The product of lead from 
pure galena does not generally exceed seventy-six to 
seventy-nine per cent. 

At the Victor-Frederick smelting works in the Hartz, one 
centner = one hundred and fourteen pounds of galena, is 
mixed with three or four times as much black flux, and with 
pyritic ores ten pounds of borax-glass are added. The 


FUSION WITH METALLIC IRON. 


383 


mixture is covered with chloride of sodium, heated for about 
twenty-five minutes in the muffle furnace with a charcoal 
fire, and then, after the mouth of the muffle has been opened 
for about five minutes, taken out of the furnace. 

3. FUSION WITH METALLIC IRON. 

Schlutter and many of the older assayers were aware that 
iron would desulphurise galena, and ever after advised the 
addition of a certain quantity of that metal to the different 
fluxes, which they used in lead assays; but it was at the 
practical School of Mines, at Montiers, that iron was first 
employed alone. 

The process is extremely convenient and easy of execu¬ 
tion ; it always succeeds, and requires no troublesome 
attention. The fusion takes place quietly, without frothing 
or bubbling : and as the whole substance employed requires 
but little space, very small pots may be employed, or a very 
large quantity assayed. But this process can only be em¬ 
ployed for pure galenas, or those which contain at most a 
few per cent, of gangue. 

When galena is heated with iron, the metal is transformed 
into protosulphide, from whence it follows, that to desul¬ 
phurise galena 22*6 per cent, is required ; but experience 
has shown that it is better to employ a little more, and 30 
per cent, can be used without inconvenience. The iron 
employed ought to be in the state of filings, or wire cut 
very small. The mixture is placed in a crucible, which is 
three-fourths filled: the whole is covered with a layer of 
salt, carbonate of soda, or black flux, and exposed to a full 
red heat. After the flux is perfectly fused, the pot may be 
cooled and broken, and a button is obtained, which at first 
sight has a homogeneous aspect, but on being struck with 
the hammer separates into two distinct parts. The lower 
part is ductile lead : the upper a very brittle matt, of a deep 
bronze colour, and slightly magnetic. Pure galena yields, 
by this process, 72 to 79 per cent, of lead, so that there is a 
considerable loss, which loss is entirely due to volatilisation. 
Berthier says that it does not appear possible to avoid this 


384 


THE ASSAY OF LEAD. 


loss, which amounts from 6 to 13 per cent., giving as a 
reason that it is probable galena begins to sublime before 
it arrives at the proper heat for decomposition. 

Antimonial galenas, or galenas mixed with iron pyrites, 
may be assayed in the same manner ; but then a sufficiency 
of iron must be added to reduce the antimony to the 
metallic state, as well as to reduce the iron pyrites to the 
minimum of sulphuration. If the galena be mixed with 
blende, the greater portion remains in the slag, because it 
is only decomposed by iron at a very high temperature. 
Blende being infusible by itself, much diminishes the fusi¬ 
bility of the matts produced ; and if it exists in very large 
quantity, it can even hinder their full fusion ; in which case, 
some protosulpliide of iron and metallic iron must be 
added to the assay, to make the slag more fusible. 

All minerals are at a minimum of sulphuration, when 
existing in matts from metallurgical works ; therefore, much 
less iron may be used in their assay than if they were pure 
ores. In very rich lead matts, in which the lead exists as 
subsulphide, from 10 to 12 per cent, is sufficient. A small 
excess of iron may be employed without inconvenience ; but 
if a larger proportion be added than is necessary to execute 
the desulphuration, the matt contains some iron in the 
metallic state, and loses its liquidity, and in consequence 
retains some globules of lead. 

The usual mode of assaying lead ores (galena) in the lead 
mills is by a modification of this process : in lieu of placing 
the ore in an earthern crucible, and adding nails or filings, 
a given weight of the ore is projected into a red-hot 
wrought-iron crucible, which is kept in the fire for about a 
quarter of an hour, or until all the galena seems decomposed. 
The lead thus reduced is poured into a mould; and if the 
scoriaceous matter be not well fused, the iron crucible is 
returned to the fire and heated still more strongly, and any 
lead that may be separated is poured into the mould and 
weighed with the rest. This is a very rude and imperfect 
process, and gives only tolerable results with pure galenas, 
but is perfectly unsatisfactory with those containing much 
earthy matter, as not above half the lead is obtained, owino- 

" 7 Q 


FUSION WITH CARBONATE OF SODA. 


385 


to volatilisation and exposure to the air, and the loss of 
globules in the slag. This process succeeds much better 
when a flux is added: this may be argol, or carbonate of 
soda, or a mixture of both (see next process). 

4. FUSION WITH CARBONATE OF SODA, OR BLACK FLUX AND 

METALLIC IRON. 

When galena is heated with an alkaline flux, out of con¬ 
tact of air, the slag contains a double sulphide of lead and 
the alkaline metal employed:'if iron be thrown into this 
Fused mixture, metallic lead separates,and the iron combines 
with the sulphur formerly combined with the lead, and the 
slag will contain a double alkaline sulphide, containing 
sulphide of iron instead of sulphide of lead, thus : 

PbS + KS + Fe=Pb + FeS + K S. 

Any earthy substances the ore may contain will be dis¬ 
solved by the alkaline flux, without very much impairing 
its fluidity. All these facts being considered, it may be 
readily seen that the assay of all earthy bodies containing 
sulphide of lead may be made in this manner, with as 
much accuracy as this method of assay can be capable of. 
Either carbonate of soda or black flux may be employed 
as the alkaline reagent, and more of either of those sub¬ 
stances must be employed, in proportion to the increased 
quantity of earthy matters the ore contains. Two parts are 
nearly always more than sufficient for poor ores, and are best 
for all cases, because an excess of flux does not diminish the 
yield of lead ; nevertheless, it is sometimes convenient to 
employ, for the latter class, but half a part. As to the iron, 
it is employed only to separate that part of the lead which 
has been dissolved in the state of sulphide by the alkali, 
but not decomposed ; so that much less may be employed 
than is necessary for the decomposition of the whole 
amount. 

Experiment has shown that the maximum amount of 
lead from pure galena may be obtained by the use of the 
following mixtures:— 


386 


THE ASSAY OF LEAD. 


2 parts of black flux, or carbonate of soda, and 10 to 12 
per cent, of iron. 

1 part of black flux, or carbonate of soda, and 20 per 
cent, of iron. 

i a part of black flux, or carbonate of soda, and from 25 
to 30 per cent, of iron. 

When black flux is employed, and the iron is in the state 
of filings, it would be inconvenient to employ too much of 
the latter, especially if the assay were heated very strongly, 
because the button of lead might be contaminated with 
iron; but when carbonate of soda is used with small iron 
nails instead of filings, the excess of iron is not inconvenient, 
but rather useful, because the desulphuration is certain to be 
complete.* 

The following changes take place in both cases. That 
portion of iron filings mixed with the carbonate of soda 
which has not been sulphuretted, is reduced to the state of 
oxide by the carbonic acid of the alkaline carbonate, and 
remains combined or suspended in the slag ; so that the 
proportion of iron is never too great, and never becomes 
mixed with the lead. When black flux is employed, the 
same oxidation does not take place, on account of the 
presence of carbonaceous matter, so that the portion of 
filings not combined with sulphur, and which is merely 
held in suspension in the flux, passes through it with the 
globules of lead to the bottom of the crucible; but if, 
instead of filings, small nails are employed, they only suffer 
corrosion at their surface, without change of form or soften¬ 
ing, and after the assay are found fixed in the surface of 
the button of lead, so that they can be detached very 
readily, and without loss of lead.f This, however, I have 
found no easy task, and have always sustained a notable 
loss. 

* The French assayers use a piece of plate iron in the shape of a horse-shoe, 
which is moved about in the melted mass until no more globules of lead 
attach themselves to it. 

In Germany a piece of iron-wire is used. What iron is not consumed by 
the assay is found still hanging together in a single mass. 

t Berthier. 


ROASTING AND REDUCING ASSAY. 


387 


5. ROASTING AND REDUCING ASSAY. 

This mode is preferable for ores and substances which 
contain a considerable quantity of foreign sulphides, or 
arsenides and antimonides, and a greater or less amount of 
earthy matter. It is used in many parts of Germany (at 
the Unterhartz), and described by Kerl thus :— 

Two assay centner of ore, matt, &c., are heated at first 
at a low red heat in the muffle, on a roasting dish that has 
been previously rubbed with chalk. After ten to fifteen 
minutes, they are taken out of the furnace, then again 
roasted at a moderate temperature for ten or fifteen minutes 
with frequent turning of the dish. The assay is then once 
more taken from the furnace, allowed to cool, rubbed up in 
an agate mortar, and again roasted for half an hour, where¬ 
upon it is taken out of the furnace ; tallow is added while 
it yet glows, and it is again brought to a strong red heat. 
The rubbing up and calcining with tallow is repeated 
several times more, and when afterwards the assays shall 
have been exposed for two hours continuously to a strong 
red heat, with the mouth of the muffle almost entirely 
closed, if no more sulphurous acid vapours escape, the roast¬ 
ing is considered as finished. This lasts from six to twelve 
hours. The roasted sample is then portioned out with the. 
balance, each portion mixed with three or four parts of 
black flux and an equal quantity of borax and glass, placed 
in a small crucible covered with chloride of sodium, 
furnished with a little piece of coal as a cover, and smelted 
in the wind furnace, for about a quarter of an hour after the 
fire is well ignited. Assays that have worked well, give 
nearly equal malleable buttons that do not contain matt, 
and a black uniformly fused slag. 

The purpose of the roasting is to convert the metallic 
sulphides, arsenides, and antimonides into oxides. But 
since in the process, sulphates, antimoniates, and arseniates 
are produced, we seek to destroy these by repeated cal¬ 
cining with tallow (see above), instead of an intermixture 
of coal-dust or flour. By melting the roasted assay with 
its charge at not too high a temperature, the oxide of lead 

c c 2 


388 


TIIE ASSAY OF LEAD. 


is reduced, and the foreign oxides and earths contained in 
the sample are, by the aid of the potash in the black flux, 
as well as of the borax and glass, slagged off. If sulphates 
or sulphides have remained behind in the roasted ore, they 
will in the smelting be partially desulphurised by the 
action of the oxides, especially of the oxide of iron. An 
addition of metallic iron would in this respect be advan¬ 
tageous. 

The roasting is a lengthy process, and one which causes 
not an unimportant loss of lead. If it is not done tho- 
roughty, then, in the reduction smelting, sulphur salts 
are formed, which always retain lead, as also a plumbifer- 
ous matt, which surrounds the lead button. By the use of 
too high a temperature in the smelting, a great part of the 
foreign oxides is reduced, and the lead becomes contamina¬ 
ted. This reduction, however, cannot be entirely avoided, 
even with a rightly conducted temperature. 

Galena melts indeed less easily if the air is excluded, than 
metallic lead; but is much more volatile than the latter, 
and is decomposed by fusion into a higher sulphide which 
is volatile and a lower one (Pb 2 S) which remains as a resi¬ 
due. By roasting, galena gives a mixture of oxide and 
sulphate of lead, from which last the sulphuric acid cannot 
be separated, even at a fusing temperature. Sulphate of 
lead becomes soft by heat, fuses at a bright white heat, and 
is converted by carbon, with a considerable loss of lead 
through volatilisation, into oxide of lead, metallic lead, or 
subsulphide of lead, according to the quantity of carbon 
used, and the temperature employed. With oxide of lead, 
the sulphate easily fuses together. 

6. ASSAY WITH SULPHURIC ACID. 

The assay sample is rubbed as fine as possible. A 
suitable quantity of it is then weighed out for an assay, and 
boiled with four to eight times its weight of oil of vitriol 
until all is decomposed. All excess of sulphuric acid is 
then evaporated in a porcelain capsule, under a flue with a 
good draught, and the mass carried to dryness. Boiling sub 


ASSAY WITH SULPHURIC ACID. 


389 


pliuric acid decomposes the sulphides, changing iron, copper, 
nickel, zinc, &c., into salts which dissolve readily in water, ' 
and also at the same time changing the sulphide of lead 
into sulphate, which in water, especially in water that is 
cold, and also contains free sulphuric acid, is practically 
insoluble, dhe composition of the ore is in general as¬ 
certained by first heating it with nitric acid or aqua regia, 
and then, with the addition of sulphuric acid, evaporating 
to dryness. The dry mass, when cold, is moistened witli a 
small quantity of sulphuric aid, then cold water; it is 
afterwards, by the aid of a small brush, brought without 
loss upon a small filter, and washed with cold water until 
the filtrate is colourless. Unnecessary prolonging of the 
washing is to be avoided, for sulphate of lead is not absolutely 
insoluble. The filter, with its contents, is dried in the 
funnel, until it can be easily taken out of it without tearing. 
It is now laid immediately into the clay crucible, in which 
the sulphate of lead is afterwards to be reduced, and this 
is placed in a very gentle stove warmth. (Some carbonate 
of potash may be first poured into the bottom of the 
crucible.) When completely dry, the crucible with the 
cover laid over it is very gently heated, so that the filter 
carbonises, which very soon happens, as the free sulphuric 
acid is not completely soaked out. The filter is now stirred 
up with a little rod, black flux or carbonate of potash with 
coal-dust and iron are introduced into the crucible, and 
intimately mixed with the sulphate of lead and the rest of 
the insoluble residue. About four or five times the volume 
of the whole residue are taken of black flux, and the assay 
is further treated, as prescribed in the portion which follows 
upon the assaying of sulphate of lead. 

In this way the lead is concentrated, and the foreign sul¬ 
phides, which were specified above as the cause of the failure 
of the assay in such cases, completely removed. The result 
obtained in this way is satisfactory, and deserves the same 
confidence as one obtained in favourable circumstances by 
the ordinary lead assay from an ore with a medium or high 
percentage of lead. 


300 


TIIE ASSAY OF LEAD. 


CLASS II. 

Assay of Substances of the Second Class .—The assay of 
these substances is very simple indeed. Litharge, minium, 
carbonate of lead, &c., may be assayed by simple fusion with 
carbonaceous matter: but when the operation is thus con¬ 
ducted loss of lead is sustained : it is therefore better to add 
some flux which will readily fuse, and allow the globules of 
reduced lead to collect into one button. No flux fulfils this 
condition better than a mixture of carbonate of soda and 
argol, which is to be intimately mixed with the assay. The 
following is the best mode of procedure :—To 200 grains of 
the finely-pulverised substance add 100 grains of argol, and 
300 of carbonate of soda, and intimately mix ; place the mix¬ 
ture iu a crucible which it about half fills, and cover with 
a layer of common salt about j inch thick; submit the 
crucible to a very gradually increasing temperature, keeping 
the heat at low redness for about a quarter of an hour ; then 
urging it to bright red until the contents of the crucible 
flow freely ; take it from the fire and shake, tap it as 
directed in the copper assay, and either pour the contents 
into the mould or allow to cool in the crucible. If the 
operator be pressed for time, the mould may be used, but 
it is recommended to allow the assay to cool in the 
crucible, for unless the operator be very careful, and have 
had some considerable practice, he is very liable to lose a 
small quantity of metal in the pouring. After the contents 
of the mould or crucible, as the case may be, are cold, the 
lead may he separated from the slag by repeated gentle blows 
from the hammer: if any of the slag or crucible adhere to 
the button, the latter may be readily freed from it by placing 
the button between the finger and thumb with its edge on 
the anvil, and then gently hammering it. The lead will be 
so altered in shape under the hammer that the slag or 
crucible readily falls off; and by continuing the process, the 
whole may be removed. The cleaned button may then be 
hammered into a cubical form, and is ready for weighing. 

In the assay of lead great care must be taken in the 


ASSAY OF SUBSTANCES OF THE SECOND CLASS. 


391 


management of the temperature, as lead is sensibly volatile 
above a bright red heat, even when covered with flux, and 
still more so if any portion be uncovered from want of 
sufficient quantity of flux; neither must the assay remain in 
after the flux flows freely, for a loss may thereby occur from 
oxidation, by decomposition of carbonate of soda, as ex¬ 
plained in the reduction of copper ores and the copper- 
refining process. 

For the rationale of this mode of assay, refer to page 
192, which explains the decomposition of oxide of lead, 
with the production of metallic lead, carbonic acid, and water, 
by the agency of a substance, like argol, containing both 
carbon and hydrogen. 

Cupel bottoms, some lead fumes, and siliceous slags, 
require a modified treatment in their assay, as the substances 
mixed with the oxide of lead (more particularly bone-ash 
in the cupel bottoms) are very infusible; and if the flux 
already mentioned as applicable to the other matters 
belonging to this class were employed, a very high tem¬ 
perature would be necessary; and as lead, as already stated, 
is sensibly volatile above a bright red heat, an evident loss 
of that metal would be the result. 

Cupel bottoms may be thus assayed : 400 grains of the 
finely-pulverised bottoms to be mixed with 200 grains of 
argol, 400 grains of carbonate of soda, and 400 grains of 
pulverised fused borax; the mixture placed in a crucible as 
already directed, covered with salt, and the fusion conducted 
as just described. 

Lead fumes and siliceous slags require only half their 
weight of fused borax, with 200 argol, 400 carbonate of 
soda, and 400 substance (fume or slag) covered with salt. 

The addition of the borax, which is a most powerful flux, 
causes the fusion of the assay to take place almost as readily 
with the last-named intractable substances, as with the 
former easily fusible and reducible matters. The assay, 
however, is rather more subject to ebullition or boiling over 
the sides of the crucible ; hence it must be carefully watched, 
and the instant it appears likely to do so the crucible must 
be removed from the fire, gently tapped on the furnace top, 


392 


THE ASSAY OF LEAD. 


and when the effervescence lias subsided returned to the 
furnace, and this operation repeated until the fusion proceeds 
tranquilly. 

The lead obtained in these assays, if the ore or substance 
contained any foreign metal, is never pure : if silver, copper, 
tin, or antimony be present, the whole of either of these metals 
will be found alloyed with the lead produced ; but if the ore 
contains zinc, and it be heated sufficiently, but a trace 
remains ; nevertheless the zinc carries off with it a consider¬ 
able quantity of lead. 

The following experiments will show what an influence 
the presence of zinc has upon the return of lead :— 

100 parts of litharge, 

100 parts of oxide of zinc, 

300 parts of black flux, 

were fused together, and 84 parts of lead were the result. 

100 parts of litharge, 

100 parts of oxide of zinc, 

600 parts of black flux, 

were fused together, and but 70 parts of lead were produced, 
instead of 90, which the pure litharge ought to have given. 
Hence it will be seen that, the more zinc is reduced, the 
more lead is volatilised. 

If oxide of iron be present in the assay, it is reduced, 
but it remains in suspension in the slag, and the lead does 
not contain a trace when it has not been too strongly heated. 
If the assay be made at a very high temperature, the iron 
may be fused, and then the lead will be ferruginous; this 
may be ascertained by means of the magnet. A similar 
result was obtained by many assayers, who thought for a 
long time that lead and iron could thus combine together ; 
but by careful examination it is easily ascertained that the 
ferruginous buttons are but mechanical mixtures of lead and 
iron in grains. Indeed, by careful hammering, nearly all 
the iron may be removed from the lead, so that it loses its 
magnetic properties. 

The oxides of maganese, when mixed with the ore, are 
changed into protoxide, which remains in the flux, and is not 
reduced. 


ASSAY OF SUBSTANCES OF THE THIRD CLASS. 


393 


Humid Assay of Ores of the Second Class. —Pulverise the 
substance very finely, and to 100 grains placed in a flask 
add one ounce of nitric acid diluted with two ounces of 
water (if minium be the substance to be analysed, it must be 
first heated to redness, so as to reduce the whole of the 
lead it contains to the state of protoxide), and gently heat, 
gradually raising the temperature to the boiling-point: when 
all action seems to have ceased, pour the contents of the 
flask into an evaporating basin, and evaporate to dryness 
with the precautions directed in the analysis of iron ore 
Allow the dry mass to cool, and a little dilute nitric acid, 
gently warm for an hour, then add water, boil, and filter. 
The whole of the lead now exists in the solution as nitrate : 
thus, say carbonate of lead had been the substance under 
analysis, then— 

Pb0,C0 2 + N0 5 =Pb0,N0 5 + C0 2 
To the filtered solution containing the nitrate as above, 
add solution of sulphate of soda, or dilute sulphuric acid, 
until no further precipitation takes place : insoluble sulphate 
of lead will now be thrown down: this must be allowed to 
completely subside by standing in a warm place ; and when 
the supernatant liquid is quite bright the sulphate may be 
collected on a filter, washed, dried in the water-bath, and 
weighed. It contains 68*28 per cent, of metallic lead. 

The decomposition of the nitrate of lead by sulphate of 
soda may be thus expressed— 

Pb + 0,N0 + JSTaO,S0 3 = Pb0,S0 3 Na0,NC0 5 . 
Determination of lead by standard solution will be described 
at the end of this chapter. 


CLASS III. 

Assay of Substances of the Third Class. —In the assay of 
bodies belonging to this class, a reducing agent must be 
employed : but if that alone be used, the sulphates and 
arseniates produce sulphides and arsenides, and not pure 
lead. The action of another reagent is therefore necessary, 



394 


THE ASSAY OF LEAD. 


in order to deprive the lead of sulphur and arsenic with which 
it is combined. 

There are two reagents known for the sulphates—they 
are the alkaline carbonates or metallic iron ; but for the 
arseniates and arsenites iron must be employed, because the 
alkaline carbonates have no action on the arsenides. 

In all cases black flux is employed: this furnishes a re¬ 
ducing agent for the oxides, and a flux for the earthy matters. 
Iron is added when the arsenites or arseniates are assayed; 
but that metal may either be employed or not, when the 
sulphates are operated upon. It is, however, always better 
to use it. 

When a mixture of black flux and iron is employed, the 
assay is made in exactly the same manner as that of the sul¬ 
phides (large nails are preferable whenever the use of iron 
is indicated in a lead assay). With the sulphate, the sulphide 
of iron formed combines in the slag with the alkaline sul¬ 
phide ; but it is not so with the arseniates and arsenites. 
The arsenide produced mixes neither with the lead nor the 
slag, but gives rise to the formation of a brittle matter 
which adheres slightly to the button of lead. 

When only black flux is employed, either of the two fol¬ 
lowing processes may be adopted :—First, the ore can be 
fused with four parts of common black flux ; then, as in the 
case of sulphide, the excess of carbon determines the 
formation of a large quantity of an alkaline sulphide ; and 
consequently produces a desulpliuration of the lead. 
Secondly, it may be fused with such a proportion of black 
flux, containing only the requisite proportion of carbon to 
reduce the oxide of lead, or with an equivalent mixture of 
carbonate of soda and charcoal. Pure sulphate of lead fused 
with one part of carbonate of soda and four per cent, of 
charcoal gives 66 of lead; but in order to employ this 
method the richness of the ore must be known, and the dry 
way is then useless, excepting for the estimation of the silver 
these substances always contain. 

Humid Assay of Substances of the Third Class .—These 
are treated in precisely the same manner as those of the 
preceding class. 



ASSAYS OF ALLOYS OF LEAD. 


395 


CLASS IY. 

ALLOYS OF LEAD. 

ASSAY WITH SULPHURIC ACID. 

No docimastic assay is known for exhibiting the lead iso¬ 
lated from its alloys. In individual cases a serviceable result 
may be attained, if the metal ( e.g . of copper by refining it) 
with which the lead is combined be determined, and its 
quantity then deducted. This method is, however, in general, 
the more unreliable, the smaller is the quantity of lead, or 
when the lead is alloyed with several metals; so that then 
the quantity of lead can often only be determined by the 
partial or complete aid of the wet way. 

Tor many products (e.g. crude lead, hard lead—containing 
antimony or arsenic—plumbiferous copper, &c.), the assay 
with sulphuric acid described on page 388 is suitable. One 
assay centner of the substance is decomposed by nitric acid 
or aqua regia, then, with the addition of sulphuric acid, 
evaporated to dryness, and the dry mass treated as above 
directed. If the residue consists only of sulphate of lead, it 
can be brought upon a weighed filter, and from the weight 
of the residue after drying, the amount of lead may be cal¬ 
culated. 100 parts sulphate of lead contain 68'33 parts 
lead. 


ADDITIONAL REMARKS ON THE LEAD ASSAY. 

Comparison of the Different Methods for the Docimastic Deter¬ 
mination of Lead in their application to various Products. 

Markus has made the following comparative experiments 
with the methods of assaying lead ores most in use at the 
Austrian smiting works at Joachimsthal. 

a. Assay with Black Flux and Iron .—One assay centner 
(5-7 grammes) of the finely rubbed, sifted, and dried assay 
substance was mixed with two assay centner of black flux 
made of sixteen saltpetre and forty argol, and sixty pounds 
of borax-glass in a mixing capsule, and put into a clay cruci¬ 
ble, on the bottom of which a piece of thick iron wire 1" inch 




39G 


THE ASSAY OF LEAD. 


long and forty centner in weight, had been placed in a verti¬ 
cal position. The crucible charge, covered over with two 
centner of decrepitated chloride of sodium, was smelted in a 
mineral coal muffle furnace, with the mouth of the muffle 
closed, and the draught half open, at a moderate temperature, 
the temperature then lowered for six to seven minutes by 
opening the mouth of the muffle, then the muffle closed again 
for an equal period, and the final heat then given. The 
cessation of the low crackling of the assay was now care¬ 
fully attended to, and this, ceasing after seven to eight 
minutes, indicated the completion of the assay. The dura¬ 
tion of the assay, by the way, was twenty minutes. 

b. Boasting and Reduction Assay with Iron. —One assay 
centner of galena was roasted, at first with a low tempera¬ 
ture, for about thirty minutes on a roasting dish, and the 
dish then pushed into the back part of the muffle for six 
to eight minutes to destroy the sulphates formed. The 
roasted ore was rubbed fine, intimately mixed with three 
hundred centner of black flux and fifty centner of borax- 
glass, placed in a crucible with a piece of iron weighing 
twenty centner at the bottom, covered with salt, and smelted 
as above. 

c. Boasting and Fusing with Black Flux. —One centner of 
the roasted ore was smelted as before with three hundred 
centner of black flux and fifty centner of borax, but without 
iron. 

The results obtained proved— 

1. That with all those products which contain tolerably 
pure sulphide of lead, especially with high percentages, the 
iron assay, a, gives in a remarkably predominant degree the 
most lead (as high as ninety-six per cent, of all the lead 
present). 

2. With impure lead ores, which contain more foreign 
sulphides, the assay a gives likewise the highest percentage, 
though the assays b and c give only a few per cent. less. 

3. If foreign sulphides are present in predominant quantity, 
the methods of b and c give a slightly higher percentage than 
that of a. 


DETERMINATION OF LEAD BY STANDARD SOLUTION. 397 


LevoVs Fusion Assay ivith Ferrocyanide and Cyanide of 

Potassium . 

According to Levol, the method of assaying galena for 
its lead by smelting it with black flux and iron is defective 
in two respects. First, it is difficult to choose precisely the 
quantity of iron required for the reduction of the lead, and 
a lack or excess of it either gives too little'lead or a button 
containing iron; and second, in order that the reaction may 
be complete and the lead unite to a button, we are compelled 
to use a very high temperature, at which lead volatilises. 
The first defect can indeed be removed by the use of iron 
crucibles, but these are easily rendered unserviceable, and 
require a pouring out of the fused mass, and then globules 
of lead are apt to remain in the slag. 

By the use of a mixture of fifty parts of cyanide of potassium 
and one hundred of anhydrous ferrocyanide of potassium to 
one hundred of galena, the loss of lead diminishes to from 
two to two and a half per cent., probably in consequence of 
the easy fusibility of the mixture and the extremely fine divi¬ 
sion of the iron in the ferrocyanide of potassium. With anti- 
monial galena this process is not applicable, as the antimony 
is reduced and goes into the lead. Cyanide of potassium alone 
gives, by reason of the greater quantity of metallic sulphide 
which it retains, a smaller product of lead. 

Schemnitz Lead Assay. 

One centner of well roasted powder is mixed with two 
centner of black flux (of one and three-quarter parts saltpetre 
and two parts argol), and six to eight centner of borax, and 
covered with a layer of chloride of sodium. 


DETERMINATION OF LEAD BY MEANS OF STANDARD SOLUTIONS. 

1. Flores Dumonte’s Method. 

Determination of Lead by means of Standard Solutions .— 
Tliis process is due to M. Flores Dumonte, and may be thus 
described :—This mode of analysis is analogous to that pro- 



398 


THE ASSAY OF LEAD. 


posed by Pelouze for the determination of copper ; ad¬ 
vantage is taken of the fact that oxide of lead is soluble in 
caustic potash in the same manner that oxide of copper 
is soluble in ammonia; and from either solution the respective 
metal is precipitated by means of a standard solution of sul¬ 
phide of sodium. 

The solution of sulphide of sodium may be conveniently 
made by dissolving one ounce of sulphide of sodium in one 
quart of water, and determining how much of it is necessary 
to precipitate twenty grains of lead. To this end weigh off 
twenty grains of lead, dissolve them in nitric acid, dilute 
with water, add excess of caustic potash until the oxide of 
lead first thrown down is completely dissolved. The solu¬ 
tion must now be heated to ebullition, and the sulphide 
of sodium gradually added from the burette: at each 
addition a black precipitate of sulphide of lead falls. The 
liquid is then boiled for a short time, by which means 
it brightens; more sulphide of sodium is then added, and 
the whole again boiled, and these operations alternately 
continued until no further coloration or blackening is 
produced by the last drop of sulphide. The number of 
divisions used is then read off, and the calculation made as 
at page 356, substituting lead for copper. 

Having thus standardised the solution of sulphide of 
sodium, the assay of a sample of ore may be thus made :— 
If the ore belong to the first class, dissolve it in dilute nitric 
acid and evaporate to dryness ; to the dry mass add excess of 
caustic potash solution, and boil; after about a quarter of an 
hour’s ebullition, filter, and throw down the lead as directed 
with the standard solution, from the amount used calculate 
the quantity of lead present; if the ore be of the second or third 
class, treat with strong nitric acid and carbonate of soda as 
already directed. The carbonate of lead so produced may 
be dissolved in either nitric or acetic acid, and to the solution 
thus obtained add caustic potash, &c. 

2. Schwartz’s Method. 

Some years ago Dr. H. Schwartz published a process for 
the volumetric estimation of lead, which consisted in pre- 


Schwartz’s method. 


399 


cipitating a lead solution (acidulated with nitric acid) by 
means of an excess of bichromate of potash ; the precipitate 
when subsided had to be washed and filtered, and precipitate 
and filter placed in a freshly prepared standard solution of 
protochloride of iron. Decomposition took place, the 
chromic acid was reduced to the state of oxide, and the 
lead converted into, and dissolved as, chloride. When 
filtered and washed, the remaining undecomposed proto¬ 
chloride of iron was estimated by permanganate of potash, 
and from the difference between the remaining and original 
amount of iron the quantity of chromic acid was calcu¬ 
lated, and in this way the amount of lead ascertained. This 
process, while it gives accurate results, requires, like that 
devised by Hempel, two filtrations and washings. 

The present process is a more direct one. Dissolve 
14'730 grammes of pure bichromate of potash in sufficient 
water to form one litre. One cubic centimetre of this solu¬ 
tion precipitates 0-0207 gramme of lead. 

In the estimation of pure lead a certain quantity of it should 
be dissolved in a minimum of nitric acid, the solution diluted 
with water, carefully neutralised with ammonia or carbonate 
of soda, and excess of acetate of soda added, and the solution 
precipitated by the bichromate of potash solution. When the 
precipitation approaches its end, or when the precipitate com¬ 
mences readily to subside, some drops of a neutral solution of 
nitrate of silver are deposited on a porcelain plate, and the 
chromate of potash solution only added by two or three drops 
at a time to the liquid under examination ; after each addition 
the whole is well stirred, allowed to subside, and a drop of 
the clear supernatant liquor added to one of the drops of the 
silver solution. As soon as the bichromate of potash is in 
excess, the two drops form a red colour, while the precipi¬ 
tated chromate of lead has no effect on the silver test, but 
simply floats on the top as a yellow precipitate. Should the 
solution assume a yellow colour before the silver reaction 
has commenced, it would indicate that not sufficient acetate 
of soda had been added in the first instance, and it would be 
necessary to add this now, and also a cubic centimetre of a 
normal lead solution, containing (H)207 of lead as nitrate. 


400 


TIIE ASSAY OF LEAD. 


The slight turbidity which first takes place soon goes off, 
and the operation may be proceeded with as before. One 
cubic centimetre must naturally, in such instance, be de¬ 
ducted from the amount of chrome solution, on account of 
the extra addition of lead. Experiments made with 0*6975 
gramme of the purest lead of Tarnowitz gave the following 
results :—They required 33*7 cubic centimetres of bichro¬ 
mate of potash solution ; when the silver reaction appeared, 
as it is always necessary to have a slight excess of bichro¬ 
mate of potash, we may assume that 33*6 cubic centi¬ 
metres were only requisite for the precipitation of the lead. 
33*6 multiplied by 0*0207 (grammes of lead) = 0*6955 
grammes, or 99*72 per cent., showing that it was nearly 
pure lead. 

0*399 grammes of well-dried nitrate of lead required also 
12*0 cubic centimetres of bichromate of potash, indicating 
0*2484 grammes of lead, or 62*29 per cent. According to 
calculation, nitrate of lead should contain 62*54 per cent, of 
lead. 

0*385 grammes of crystallised acetate of lead required 
10*2 cubic centimetres of chrome solution = to 0*211 
grammes, or 54*84 per cent, of lead, while according to 
the formula PbOA + 3HOit should have been 54*61 per 
cent. 

Of all foreign metals bismuth alone seems to interfere 
with the reaction, and behave very like lead with chromic 
acid, and if present it requires a more suitable mode of pro¬ 
ceeding. Tin and antimony are converted into insoluble 
oxides during the solution of the lead in nitric acid, while 
arsenious acid offers no difficulties, but if desired it may be 
separated from the lead as sulphide with sulphide of am¬ 
monium. Arseniate of lead is insoluble in an acetic 
solution, and only partly decomposed by bichromate of 
potash, and the removal as sulphide in such instance becomes 
necessary. Gold and platinum are insoluble in nitric 
acid. 

The'presence of silver is of no great importance ; during 
the operation the lead is first thrown down as a yellow 
precipitate, and afterwards the precipitation of the silver 



hempel’s METHOD. 401 

takes place, giving the red reaction similar to the silver test 
always resorted to. It may, however, be separated from 
the lead solution by means of chloride of sodium, and the 
chloride of silver either filtered off, or in case not too much 
chloride of sodium has been used, left in the solution, and 
the lead estimated as usual. Chloride of lead is tolerably 
soluble in hot water, and chromate of lead is not decomposed 
by chloride of sodium ; this, however, is the case with 
chromate of silver. 

The higher oxide of mercury is not precipitated by bi¬ 
chromate of potash, not even in an acetic solution, while 
the lower oxide is; and, as it is difficult to peroxidise 
all the mercury when united with lead, even by long- 
continued boiling in nitric acid, it becomes necessary to 
evaporate and calcine the residue till all the mercury 
is volatilised. To obviate the formation of red lead, the 
calcined residue has to be moistened with a few drops 
of oxalic acid, and again dried and carefully calcined 
and dissolved in acetic acid ; after this, the lead may be 
estimated as usual. To avoid the above calcinations, the 
mercury may be precipitated from the nitric acid solution 
by means of hydrochloric acid, and the calomel boiled till 
it is converted into the higher chloride. 

Copper, cadmium, zinc, iron, and cobalt do not in the 
least interfere with the reaction, provided the iron is per- 
oxidised. Of the different acids, hydrochloric acid some¬ 
what disturbs the last silver reaction, but by using larger 
drops, and allowing the reaction of chloride of silver to go 
off, we obtain the usual chromate of silver reaction. 

Sulphate of lead has first to be converted into the state of 
carbonate, by boiling with carbonate of soda, when it may 
be dissolved in acetic acid. Phosphate and arsenite of lead, 
or other lead salts insoluble in acetic acid, may be dissolved 
in nitric acid, and estimated according to my older method. 

3. Hempel’s Method (modified). 

Mr. Sutton thus describes this method :—The lead 
solution, which must contain no other body precipitable by 
oxalic acid, is put into a 300 cc flask, and a measured 

D D 



402 


TIIE ASSAY OF LEAD. 


quantity of normal oxalic acid added in excess; ammonia 
is then added to slight predominance, the flask fdled to 
the mark with water, shaken, and put aside to settle ; 100 cc 
of the clear liquid may then be taken, acidified with 
sulphuric acid, and titrated for the excess of oxalic acid 
with permanganate; the amount so found multiplied by 
3 and deducted from that originally added will give the 
quantity combined with the lead. 

Where the nature of the filtrate is such that perman¬ 
ganate cannot be used for titration, the precipitate must be 
collected, well washed, dissolved in dilute nitric acid, sul¬ 
phuric acid added, and titrated with permanganate. 

In neither case are the results absolutely accurate, owing 
to the slight solubility of the precipitate, but with careful 
manipulation the error need not exceed 1 per cent. 

The following investigations of M. Levol will be found 
of interest. The author has investigated the subject of the 
quantitative determination of lead. He admits that the 
precise estimation of lead, though presenting no serious 
difficulties, nevertheless demands precautions sufficiently 
minute. 

The estimation of lead in the state of sulphate , by means of 
sulphuric acid and evaporating to dryness, insures accuracy, 
but the process requires con tan t attention. Towards the 
end of the analysis the evaporation exposes it to loss by pro¬ 
jection ; moreover, if the liquids contain iron, the sulphate 
of lead is often contaminated with the slightly soluble ferric 
sulphate. The solubility of sulphate of lead, even in water, 
is well known, as the following experiment shows :—Preci¬ 
pitate one equivalent of nitrate of lead by two equivalents 
of sulphuric acid diluted largely with water ; then wash 
during several days, and long after the washings have 
ceased to redden litmus-paper, they will still become slightly 
turbid by nitrate of baryta and hydrosulphate of ammonia. 

The use of soluble sulphates , suggested by various authors, 
is not to be recommended, as will be shown. 

M. Levol’s opinion was, that the principal inconvenience 
arose from the incomplete insolubility of sulphate of 
lead, and that, consequently, the employment of alkaline 


lkvol’s method. 


403 


sulphates would produce but imperfect results. He was 
then much surprised to find, under such circumstances that 
the fact could not escape notice, an overweight in preci¬ 
pitating lead by sulphate of potash. If, in fact, liquids much 
charged with nitrate of lead and sulphate of potash or soda 
in excess are put in contact, precipitates are obtained, the 
weight of which considerably exceeds that of the sulphate 
of lead, corresponding to the weight of nitrate, and it is with 
difficulty that they are reduced to this weight by washing. 

These are some of the results:—5T775 grammes (= 1 
equivalent) of nitrate of lead, added to 5*455 grammes 
( = 2 equivalents) of sulphate of potash, yielded a precipitate 
which simply drained, then dried at 110° and weighed on 
the filter, yielded 7*355 grammes, instead of 4*739 grammes. 
This precipitate was fusible, and to separate from it the sul¬ 
phate it contained, no less than ninety washings in cold water 
were required. 

An experiment made with nitrate of lead and sulphate 
of soda yielded 5*325 grammes of dried precipitate, 
instead of 4*739 grammes; and to extract from it the sul¬ 
phate of soda thirty-six washings in cold water were 
necessary. 

It seems evident that in both cases there must have 
been a formation of double sulphates, while that of potash 
appears to have been by far the most stable, the over¬ 
weight of sulphate of potash being 2*616 grammes. (The 
formula Pb0,S0 3 + K0,S0 3 would require 2*686 grins.) 
With the sulphate of soda, the overweight = 0*586 
gramme, which represents about one-third of the equi¬ 
valent. The formula Pb0,S0 3 4- JSTa0,S0 3 requires 1*704 
grammes. 

After prolonged washing the sulphate of lead precipitated 
by sulphate of soda weighed 4*640 grammes, the loss by 
washing 1 laving been 0*099 gramme. 

The previous precipitate = 4-585 grammes. 

Loss by washiugs = 0-154 „ 

Independently of less stability, this difference seems to 
indicate greater solubility of the double sulphate of lead 
and soda, which is further rendered apparent by testing the 

D D 2 


404 


THE ASSAY OF LEAD. 


washings by means of baryta and hydrosulphate of am¬ 
monia (apart from the solubility proper to the sulphate of 
lead, which was taken into account in this instance), by 
comparing with it a third washing of sulphate of lead, 
formed by sulphuric acid and nitrate of lead, equivalent to 
equivalent. 

It appears, then, that there are formed by the wet way, 
under certain conditions, double sulphates of lead and potash 
or soda. 

On the whole, then, experience shows that alkaline sul¬ 
phates should not be applied to the estimation of lead in the 
state of sulphate, by weighing the precipitate, partly because 
of the danger about to be described, and partly because 
of the fear of loss of sulphate of lead, by the numerous 
washings necessitated by the decomposition of the double 
salts by water. 

Determination of Lead in the State of Carbonate.— In 

face of the difficulties to be encountered in estimating lead 
with great precision, it seems highly to be recommended 
that it should be determined in the state of carbonate: for 
that purpose ordinary carbonate of ammonia, to which is 
added caustic ammonia, is used. The object of this addition 
is to avoid the employment of too large a volume of solution 
of carbonate of ammonia, a salt not very soluble in water. 
Ammonia forms, with nitrate of lead for instance, a very 
incomplete precipitate. It would not, then, be prudent to 
divide the operation into two—that is to' say, by employing 
ammonia first to saturate the liquid—and consequently it 
should not be poured in until it has been charged with 
carbonate of ammonia, which it dissolves abundantly and 
easily. The precipitate separates perfectly from the liquid, 
is easily collected and dried on a filter. The deposition of 
the precipitate is completed in about twenty-four hours, 
especially under the influence of gentle heat. According to 
the writer’s experience, two or three thousandths of lead can 
be estimated by this process. 

The precipitate, which is anhydrous, PbO,C0 2 , is deposited 
on a small double filter, each one of the same weight. 

If, as frequently happens, in analysing metallic substances, 


BLOWPIPE REACTIONS OF LEAD. 


405 


tlie colour, which should be pure white, is yellowish, it is 
owing to the presence of iron, which is easily got rid of by 
washing the filter after, weighing, with water acidulated with 
sulphuric acid. 

It there is reason to suspect the presence of bismuth, treat 
a small quantity of the weighed precipitate with a little nitric 
acid. A few drops of iodide of potassium in the liquid 
will detect the presence of bismuth by the formation of a 
brown precipitate, or yellow-brown if there is bismuth and 
lead. The latter metal, when present alone, gives a pure 
yellow precipitate. 

Determination of Lead by Oxalic Acid.— In estimating 

© 

lead by carbonate of ammonia, in presence of an excess of 
ammonia, two or three thousandths of this metal can be 
determined. By operating, under the same conditions , with 
oxalic acid, it has been found impossible to determine it to 
less than 1 per cent. Writers have, indeed, observed, that 
the precipitation of lead by oxalic acid should be effected 
in neutral liquids ; but this necessity but ill agrees with the 
most ordinary instances of the analysis of metallic sub¬ 
stances, where the presence of an excess of ammonia is 
indispensable for maintaining in solution certain substances 
from which the lead should be separated. 

BLOWPIPE REACTIONS OF LEAD. 

When plumbiferous compounds which are met with in 
nature, and furnace products, are treated on charcoal, in the 
oxidising flame, they give a sublimate which is very easily 
recognised. Other easily volatilised metals, which may be in 
combination with the lead, either fume away entirely, or else 
deposit an oxide upon the support. The oxide of lead sub¬ 
limate, which is dark lemon-yellow while hot, and sulphur- 
yellow when cold, deposits nearer to the assay than the subli¬ 
mates of some other metallic oxides, namely, those of tellurium, 
selenium, antimony, and arsenic, and is by this means dis¬ 
tinguished. Should zinc also be an ingredient, the sublimate 
of oxide of lead will probably be contaminated with a 
quantity of the oxide of this metal, but the sulphur-yellow 


40 r> 


BLOWPIPE REACTIONS OF LEAD. 


colour of the lead deposit cannot be mistaken, when the 
assay has perfectly cooled. 

Oxide of Lead. — Alone , minium blackens when heated, 
and is transformed into the yellow oxide. It forms by fusion 
a fine orange glass, which is reduced with effervescence on 
charcoal. 

With borax it fuses readily on the platinum wire, and 
gives a transparent glass, which, when saturated and hot, is 
yellowish, but which becomes colourless on cooling. It is 
reduced on charcoal. 

With microcosmic salt it readily fuses into a transparent 
and colourless glass. 

With socla , oxide of lead readily fuses on the platinum 
wire, forming a transparent glass, which becomes yellowish 
and opaque by cooling. Its reduction takes place instan¬ 
taneously on charcoal. 


ORES OF LEAD. 

Sulphide of Lead, Galena.— Alone , on charcoal, it does 
not fuse until after disengagement of sulphur; globules 
of lead then form on the surface, and finally a bead of 
lead is obtained. By cupelling this, the presence of silver 
may be ascertained. After cupellation, the bone-ash 
indicates by its colour whether the lead were pure or 
not; if it were, when cold the cupel would be pure yellow; 
copper renders it green, and iron brown or blackish. 

In the tube , galena gives off sulphur, and a white subli¬ 
mate of sulphate of lead. 

Oxide of Lead. — Its action with fluxes has been already 
shown. 

Sulphate of Lead decrepitates, and fuses on charcoal in the 
outer flame into a transparent bead, which becomes milky 
by cooling. In the reducing flame it effervesces, giving a 
button of lead. 

Carbonate of Lead behaves like oxide of lead. 

Phosphate of Lead.— Alone , on charcoal, it fuses, the 
bead crystallising as it cools. The crystals have large facets, 
and a pearly whiteness. 

With fluxes it behaves like oxide of lead. 



407 


CHAPTER XI. 

THE ASSAY OF TIX. 

This metal is always found by the assayer in the state of 
oxide. 

Oxide of Tin (Sn0. 2 ).—The appearance of this mineral 
gives no indication, excepting to an experienced eye, that 
metallic matter enters largely into its composition ; yet its 
great density would lead one to suppose such to be the 
case. Its colour varies from limpid yellowish white to 
brownish black and opaque, passing from one to the other 
by all intermediate shades. It usually possesses a peculiar 
kind of lustre which cannot be readily described, but once 
seen can scarcely be mistaken. It occurs crystallised in 
square prisms, terminated by more or less complicated 
pyramids. These crystals, derived from the octahedron, 
are often macled or hemitropic, so that they often possess re¬ 
entrant angles, which is to a certain extent characteristic. 
The principal varieties are the following:— 

1. Crystallised Oxide of Tin is found in more or less 
voluminous crystals of the colour and form as above. 

2. Disseminated Oxide of Tin. —This variety occurs 
in grains of various sizes, sometimes so small as not to be 
visible to the naked eye. It is found in the primitive 
rocks. 

3. Sandy Oxide of Tin forms pulverulent masses often of 
great extent; in appearance it is merely a brown sand. 

4. Concretionary Oxide of Tin , Wood Tin. —This variety 
occurs in small mamellated masses, the fibrous texture of 
which resembles that of wood : hence the name. 



408 


TIIE ASSAY OF TIN. 


The following is an analysis of a sample of oxide of tin 
from Cornwall:— 


Oxygen 
Iron . 
Silica 


Tin . 


. 77*50 
. 21-40 


•25 

•75 


Assay of Pure Oxide of Tin .—Pure oxide of tin may be 
very readily assayed in the following manner :—Weigh off 
400 grains, place them in either a black-lead or charcoal-lined 
crucible, cement on a cover by means of Stourbridge clay, 
and subject to the fire. The heat should for the first quarter 
of an hour be a dull red, after which it may be raised to a 
full bright red for ten minutes, and the crucible removed 
with care so as not to agitate or disturb the contents; 
tapping in this case must not be resorted to. When the 
crucible is cold, remove the cover, and a button of pure tin 
will result: this weighed and divided by four gives the per¬ 
centage. If the operation has not been carefully conducted, 
it sometimes happens the tin is not in one button, but dis¬ 
seminated in globules either on the charcoal lining or on the 
sides oi the black-lead pot; in this case the charcoal on the 
one hand, or the black-lead crucible on the other, must be 
pulverised in the mortar and passed through a sieve ; the 
flattened particles of tin will be retained by the sieve, and 
can be collected and weighed. If any small particles 
escape the sieve, they may be separated from the lining or 
crucible by vanning. 

If a charcoal or black-lead crucible be not at hand, an 
ordinary clay pot may be used, but not so successfully, ex¬ 
cepting under certain circumstances to be hereafter described. 
Indeed, in Cornwall the ordinary mode of conducting this 
assay is in a naked crucible, thus : About 2 ounces of the 
ore are mixed with a small quantity of culm, and projected 
into a red-hot crucible. If the ore seems to fuse or work 
sluggishly, a little fluor-spar is added, and after about a 
quarter of an hour’s fusing at a good high temperature, the 
reduced and fused tin is poured into a small insot mould, 
and tiie slag examined for metal by pounding and vanning. 
This method never gives the whole of the metal. To effect 


ASSAY OF PURE OXIDE OF TIN. 


409 


this, without fear of mischance in the assay sometimes 
occurring as already described, with both black-lead and 
charcoal lined crucibles, it may be thus conducted; always 
supposing the oxide to be pure, or nearly so, or at least 
containing little or no siliceous matter. 

To 400 grains of ore add 100 grains of argol, 300 grains 
of carbonate of soda, and 50 grains of lime; mix well to¬ 
gether, place in a crucible which the mixture half fills, 
cover with a small quantity of carbonate of soda and 200 
grains of borax. Place the whole in the furnace with the 
necessary precautions, raise the heat very gently, and keep 
it at or below a dull red heat for at least twenty minutes; 
then gradually increase until the whole flows freely. Be- 
move the crucible, tap it as for copper assay, and allow to 
cool. When cold, break it, and a button of pure metallic 
tin will be found at the bottom, and a flux perfectly free 
from globules and containing no tin. 

There is yet another process, which is more easy of exe¬ 
cution ; but the reagent employed is more expensive, not so 
readily obtainable, and more difficult to keep without de¬ 
composing than any of the substances above employed. 
The reagent now to be discussed has been introduced to the 
notice of the student, in another part of this volume, as a 
blowpipe flux, and in the assay of copper ores by standard 
solutions, as cyanide of .potassium. This is the most 
effective reducing flux for tin ores yet known. It acts by 
absorbing oxygen to form a compound known as cyanate of 
potash : thus— 

Sn0 2 + KCy=Sn + KO,Cy O. 

The assay, by means of this substance, may be made in 
ten minutes. 

This method of estimating the value of tin-stone has 
been frequently practised by the writer during the last nine 
years, and lias uniformly furnished correct results with 
but little expenditure of time and labour. The method of 
operating is as follows:—The sample having been care¬ 
fully selected, is first crushed by the hammer in a steel 
mortar, and then further reduced to powder in an agate 


410 


THE ASSAY OF TIX. 


mortar. 100 grains is a convenient quantity to be taken 
for analysis, and it is always advisable to make two inde¬ 
pendent experiments upon the same sample of ore, with 
the view of having a control, and the highest result obtained 
is that upon which to place reliance, since the error must 
always be on the side of loss rather than excess. A couple 
of small Hessian crucibles, of about 3 oz. capacity, are pre¬ 
pared in the first instance by ramming into the bottom 
of them a small charge of powdered cyanide of potassium 
sufficient to form a layer of about half an inch in depth; 
the weighed quantities of tin ore are then intimately mixed 
with from four to five times their weight of the powdered 
cyanide, and the mortar rinsed with a small quantity of the 
pure flux, which is laid upon the top of the mixture. The 
crucibles are then heated in a moderate fire, or over a gas- 
blowpipe, and kept for the space of ten minutes at a steady 
fusion; they are then removed, gently tapped to facilitate 
the formation of a single button, and allowed to cool. Upon 
breaking the crucibles, the reduced metal should present an 
almost silvery lustre, with a clean upper layer of melted 
flux. It is advisable to dissolve the latter in water, in order 
to be certain as to the absence of any trace of reduced metal 
or heavy particles of the original ore. There is always 
contained in the commercial cyanide a sufficient quantity of 
alkaline carbonate to secure the perfect fusion of the silicious 
gangue and other like impurities in the tin ore, but the ope¬ 
rator should assure himself of the absence of copper and 
lead in the ore, either by preliminary treatment with hydro¬ 
chloric acid, in which tin-stone is absolute insoluble, or by 
testing the button of reduced tin after hammering or rolling 
for such metallic admixture. We have usually found a 
minute trace of iron, and sometimes gold, in the melted 
buttons, but not so much as to add appreciably to their 
weight. 

When worked with ordinary care, this process may be 
relied upon as giving numbers true to within \ per cent., 
and we do not know any other method which exceeds this 
in accuracy and rapidity of execution. The following are a 


ASSAY OF FURE OXIDE OF TIX. 


411 


few analytical results taken at random from a number of 
ores assayed in this manner :— 

Tin per cent. 

. - ' - ^ 

I. II. 

Sample No. 1 . 45*6 45-8 

„ No. 2. 57-2 57-6 

„ No. 3.C8-4 68-7 

Dr. Clemens Winkler mentions the well-known difficulty 
of obtaining all the tin in one button in a dry assay by the 
ordinary process, and the error of 5 or 10 per cent, which 
arises. To avoid this loss, he suggests the addition of copper 
for the purpose of collecting together the tin, and states 
that he has obtained tolerably accurate results by the fol¬ 
lowing process:— 

The ore is finely pulverised and roasted, first by itself 
and then once or twice with charcoal or coke, to remove 
sulphur, arsenic, and antimony. The residue is then di¬ 
gested for a quarter or half an hour with hot hydrochloric 
acid, and afterwards well washed with hot water. Iron, 
manganese, and copper, he states, are more completely re¬ 
moved by fusion with bisulphate of potash, and then treating 
with hydrochloric acid, and washing with water. Tungstic 
acid, if present, will now be removed by digesting with 
caustic potash or ammonia. 

The oxide of tin, silica, &c., remaining is now mixed in 
a crucible with an equal weight of oxide of copper, and 
two or three parts of flux, consisting of two parts anhydrous 
carbonate of soda, one part white flour, and a quarter part 
borax glass. The whole is then covered with a layer of 
common salt, upon which a piece of charcoal is laid. The 
crucible is then heated first to a red and then to a dull white 
heat for an hour after, which a button containing the whole 
of the reduced tin and copper will be found at the bottom. 

As pure oxide of copper may not be obtainable, the 
author recommends that a portion of every sample should 
be separately assayed. The weight of the tin will be found 
by subtracting the weight of the copper from that of the 
button. 

Assay of Oxide of Tin mixed with Silica .—Although 



412 


THE ASSAY OF TIN. 


oxide of tin is completely reducible by charcoal or othel 

carbonaceous matter, yet it lias such an affinity for silica, 

that whenever that substance is present, the metal cannot 

be wholly reduced, excepting at the highest temperature of 

a wind furnace. The following experiments will show the 

influence of silica on the return of tin in an assay of oxide 

of that metal with black flux :— 

Ore 100 100 100 100 100 

Quartz 25 6G 100 150 300 

The first gave 52 per cent, of tin; the second, 43 per 
cent.; the third, 28 per cent.; the fourth, 10 per cent.; and 
the last nothing. 

The slags also produced in the treatment of tin ores in 
the large way give no return with black flux. This mode 
of assa} r , however, has been recommended by some, but 
from the foregone experiments, is proved to be perfectly 
fallacious: that is, unless the quantity of silica present be 
very small in comparison to the amount of oxide of tin; 
and even when the latter is present in four times the quan¬ 
tity of the silica, as in experiment No. 1, a loss of 20 per 
cent, of tin is sustained. 

Assay of Tin Ores containing Silica and Tin Slags .—It 
having just been shown how injuriously the presence of 
silica influences the produce of tin, both in ores and slags, 
other methods of assay than those just described must be 
adopted for such substances. These will be now detailed. 

Tin ores containing silica may be treated by two methods : 
in the first the silica must be carefully separated by vanning ; 
if the ore be well pulverised this is the best and most expe¬ 
ditious method. In conducting this assay take 400 or more 
grains of the pulverised ore according to its richness (if poor, 
as much as 2,000 grains may be taken), van in carefully, 
dry the enriched product, which will, if the operation has 
been properly conducted, be nearly pure oxide of tin, and 
assay it as already described for ores containing no silica. 
The other process of assay may be thus conducted, and is 
dependent upon the fact that iron displaces tin in its combi¬ 
nation with silica : thus, if a compound of oxide of tin and 
silica be heated to whiteness with metallic iron, a portion of 


ASSAY OF TIN ORES CONTAINING ARSENIC, ETC. 


413 


the iron oxidises and replaces the oxide of tin, which was 
previously in combination with the silica as a silicate of tin, 
and metallic tin and silicate of iron result, the tin so reduced 
combining with any metallic iron that may be in excess, 
and the button thus obtained is an alloy of tin and iron, 
whilst the slag is entirely deprived of tin. 

In this kind of assay mix 400 grains of the silicated 
oxide of tin with 200 grains of oxide of iron (either pulver¬ 
ised haematite or forge-scales will answer this purpose), 100 
grains of pounded fluor-spar, and 100 grains of charcoal 
powder; place the mixture in a crucible, and cover with a 
lid, gradually heat to dull redness, and keep at that tempera¬ 
ture for half an hour, then heat to whiteness for another 
half hour, and remove the crucible from the furnace, allow 
to cool, and break. The button so obtained is to be treated 
in the humid way, as hereafter described. 

The assay of tin slags is conducted in the same manner, 
or simply by mixing the pulverised slag with 20 per cent, 
of iron filings, and fusing. 

Assay of Tin Ores containing Arsenic , Sulphur , and 
Tungsten {Wolfram). —In the assa} 7 of such ores it is neces¬ 
sary to remove arsenic, sulphur, and tungsten, before at¬ 
tempting to obtain the tin in a pure state by dry assay. 
Ores of tin which contain either one or all of these substances 
are most common: hence this mode of treatment will be 
generally required. 

Most assayers usually submit the ore to the same mode of 
treatment which it undergoes on the large scale by calcination, 
or rather roasting, by which the greater part of the arsenical 
and pyritic matter is removed ; this process fails, however, 
to remove the whole of these substances, and does not at all 
affect the tungsten. The following process, adopted by the 
author, is therefore preferable, and is founded on the fact 
that arsenical and other pyrites, as well as tungstate of iron 
(wolfram usually accompanying tin ores), are completely 
decomposed by nitro-hydrochloric acid {aqua regia) at the 
boiling temperature, the oxide of tin alone not being 
affected :—Take 400 grains or more of the impure tin sample, 
place them in a flask, and add 1}> ounce of hydrochloric 


414 


THE ASSAY OF TIN. 


acid, and b an ounce of nitric acid, heat gently for about 
half an hour, and then boil until the greater part of the 
mixed acids have evaporated; the sulphur and arsenic will 
by this time be converted into sulphuric and arsenic acid, 
and the wolfram completely decomposed, its iron and 
manganese having become soluble, and its tungstic acid 
remaining in the insoluble state with the oxide of tin and 
any silica that may be present. Allow the flask and con¬ 
tents to cool, add water, allow to settle, and decant, and so 
on until the water passes off tasteless. The insoluble matter 
in the flask is now oxide of tin, silica, and tungstic acid ; to 
remove the latter, digest for an hour at a very gentle heat 
with one ounce of solution of caustic ammonia, with 
occasional agitation; add water, and van the remainder to 
separate silica; nothing remains now but oxide of tin with 
perhaps a little silica : this is now to be dried and assayed 
as directed for ores containing little or no silica. 

If only an approximative assay be needed, it may be ac¬ 
complished after this treatment by taking the specific gravity 
of the remaining oxide, so that all ores of tin may be thus 
roughly assayed, it being premised that the above operation 
has been so carefully performed that nothing but oxide of tin 
and silica remain. The specific gravity of the thus purified 
ore is to be taken. All now that is necessary to be known is 
the specific gravity of oxide of tin, its percentage of pure 
tin, and the specific gravity of silica, and at simple calcula¬ 
tion gives the result. The following is the formula :— 


Let a represent the specific gravity of oxide of tin. 


v 

v 


b 

c 

V) 

X 

y 


V 

V 


V 

V 


V 


silica. 

the mixture left after treatment 
with acid, &c. 
weight of rough oxide of tin or mixture left after 
treatment with acid, &c. 

„ oxide of tin. 

„ silica. 


Then a' =. " (°— 6 ) 
c (a — b ) 


w ; 




ESTIMATION OF TIN IN THE WET WAT. 


415 


Or in arithmetical form thus,— 

1. From the specific gravity of the rough oxide of tin (mixture of oxide of 
tin and silica) deduct the specific gravity of the silica. 

2. Multiply the remainder by the specific gravity of the oxide of tin. 

3. Multiply the weight of the rough oxide of tin by the last product, which 
will make a second product which may be called P. 

4. From the specific gravity of oxide of tin deduct the specific gravity of 
silica. 

5. Multiply the difference by the specific gravity of the rough oxide of tin. 

6. Take this product for a divisor to divide the above product P : the 
quotient will be the weight of pure oxide of tin in the rough oxide, and the 
quantity of metal can now be readily calculated. 


The following is an assay worked out in this manner :— 

400 grains of the ore are treated with nitro-hydrochloric acid and ammonia 
as above described, washed and dried. Suppose the dried matter weighed 
250 grains. The 250 grains thus obtained are placed in the specific gravity 
bottle, and the specific gravity is found to be 5-4. 

Specific gravity of tin oxide (approximate) . . . 6-9 


, silica 

V 

• 

Sp. Gr. 
Rough Oxide 

5-4 


Sp. Gr. 

Silica 

2-6 = 

2-8 

2-8 

X 

Sp. Gr. 

Pure Oxide 

6-9 = 

19-32 

Weight of 
Rough Oxide 

250 

X 

19-32 - 

p 

4830 

Sp. Gr. 
Pure Oxide 

6-9 


Sp. Gr. 

Silica 

2-6 = 

4-3 

4-3 

X 

Sp. Gr. 

Rough Oxide 

5-4 = 

23-22 


4830 

23-22 


= 208-4 


208-4 grains is therefore the weight of pure oxide in the 400 grains of ore. 
Now oxide of tin contains 78-01 parts of pure tin, and a 


208-4x78-61 
100 


= 163-72 


So that 400 grains of rough tin ore contain 163-72 grains of pure tin, and 

l^ 72 = 40-93. 


The rough sample first operated on contains, therefore, 
40-93 per cent, of metallic tin. 

Estimation of Tin by the Humid Method .—There are 
several methods of effecting this analysis, the chief difficulty 
being found in the intractable nature of the oxide of tin, it 







416 


THE ASSAY OF TIN. 


resisting the action of all acids. This, however, may be 
overcome as first shown by Klaproth, who found that very 
finely levigated oxide of tin was soluble in hydrochloric 
acid after a prolonged fusion with caustic potash : the fol¬ 
lowing is his process :— 

Fifty grains of the tin ore, reduced to the most minute 
state of division by levigation or otherwise, is mixed with 
four times its weight of caustic potash. The best mode of 
mixing is to place the caustic potash in a silver crucible, 
add its own weight of water, and apply a gentle heat until 
the potash is dissolved; then stir in tin ore, and gradually 
evaporate to dryness, stirring all the time to prevent loss by 
spitting, as in the analysis of iron stone : when thoroughly 
dry, enclose the silver crucible in one of clay, and submit 
the whole to a dull red heat for at least half an hour : rather 
more than less renders the perfect solution of the oxide of 
tin more certain. When cold, act on the contents of the 
crucible with dilute hydrochloric acid, transfer the liquid 
and any undissolved matter to a flask, add some strong 
hydrochloric acid, and boil for half an hour. If at the end 
of this time any of the tin ore remains unacted on, it must 
be separated by decantation or otherwise from the solution, 
dried, again fused with potash, and then treated with hy¬ 
drochloric acid, in which it will now be found totally soluble. 
This second operation will not be needed if care has been 
taken to reduce the ore to the finest possible state of di¬ 
vision at first. The solution, however obtained, is to be 
evaporated to dryness, and when cold treated with a small 
quantity of hydrochloric acid, allowed to stand for half an 
hour, then water added, boiled and filtered: the whole of 
the tin will pass through in solution as chloride of tin, and 
any silica or tungstic acid that may be present will remain 
in the filter. If the ore contained copper, lead, and iron, 
these metals will also be in solution—at all events, the lead 
partially so; but if the ore had, previously to its fusion with 
caustic potash, been treated with aqua regia , as already 
described, then it will contain tin alone. It is always better 
thus to separate foreign matters before attempting the so¬ 
lution of the tin, as the after process is thereby simplified. 



ESTIMATION OF TIN BY MEANS OF A STANDARD SOLUTION. 417 

Supposing, however, that the rough ore had been submitted 
to fusion with potash and then dissolved, the solution must 
be thus treated :—A bar of zinc must be placed in the 
solution, which will in course of time precipitate tin, copper, 
and lead; when all the metals are thus thrown down the 
zinc is washed and removed, the precipitated metals well 
washed and dried. To the dried metals strong nitric acid 
is now to be added, the mass gently heated, and then 
evaporated to dryness: when cold, it is moistened with 
dilute nitric acid, water added, and the whole filtered. 
Lead and copper will pass through the filter as soluble 
nitrates, and the tin will be found in the filter as insoluble 
peroxide ; this is to be well washed, dried, ignited, and 
weighed. It contains 78*61 parts of metallic tin. The 
amount of tin thus obtained, when multiplied by two, will 
represent the percentage of the ore. 

If, before the action of caustic potash, the ore had been 
submitted to the action of aqua regia , sulphuretted hy¬ 
drogen may be passed through the solution of chloride of 
tin, when sulphide of tin will be precipitated; this is to be 
washed, dried, gently calcined in a platinum crucible until 
all smell of sulphurous acid has ceased, allowed to cool, 
reheated with a fragment of carbonate of ammonia, as in 
the case of roasting sulphide of copper, and when cold 
weighed as pure oxide of tin. The calculation for metal is 
made as above. 

Humid Analysis of the Alloy of Tin and Iron as ob¬ 
tained in the Treatment of Siliceous Ores and Slags. —The 
alloy obtained as already directed is dissolved in boiling 
hydrochloric acid, diluted with water, and the solution, if 
necessary, filtered. To the filtered solution add a little 
hydrochloric acid and pass an excess of sulphuretted hy¬ 
drogen through it, collect the precipitated sulphide of tin, 
and proceed according to the directions already given. 

Estimation of Tin by means of a Standard Solution .— 
The first process to be described is due to M. Gaultier de 
Claubry, and may be thus performed:—The standard solution 
is made by dissolving 100 grains of iodine in 1 quart of 
proof spirit (spirit of wine having a specific gravity of *920), 

E E 



418 


THE ASSAY OF TIN. 


and is thus standardised. Ten grains of pure tin are dis¬ 
solved in excess of hydrochloric acid, the solution boiled, 
and allowed to cool: the burette is now filled with the 
solution of iodine, which is gradually added to that of the 
tin until the former ceases to be decolorised: as soon, there¬ 
fore, as the tin solution assumes a faint yellow tinge, 
sufficient iodine has been added : the quantity thus found 
sufficient is then noted, and the amount of tin each division¬ 
ful of iodine solution is equivalent to, is calculated as for 
iron, copper, and the other standard solutions. 

In the actual assay of tin ore by means of this solution it 
is necessary the whole of the tin present be reduced to the 
state of protochloride: this may be readily effected by 
boiling the solution of tin for a quarter of an hour with 
excess of metallic iron, and filtering. To the solution so 
obtained the iodine- is added as above. The tin ore is dis¬ 
solved by any of the methods already described. 

M. Scheurer Kestner, of Thann, has devoted some at¬ 
tention to this subject. His process depends on the trans¬ 
formation of protochloride of tin into bichloride. MM. 
Streng and Mohr * have employed bichromate of potash, 
solution of iodine, and permanganate of potash as oxidising 
agents. The result of M. Mohr’s experiments is that which¬ 
ever of these bodies is employed, the proportion found 
varies with the quantities of water used, so that upon taking 
certain quantity of chemically pure tin, the trials made with 
permanganate of potash, or any other oxidiser, will not 
give the weight of tin employed, but always a less weight—a 
circumstance which has induced him to admit for these 
estimates an empirical atomic weight for tin (65), differing 
greatly from the actual weight (59). Even this number is 
allowable only when operating constantly with quantities of 
water equal to those which served to determine it. 

M. Lenssenf estimates tin by means of the iodine solution, 
but he operates in a liquid containing double tartrate of 
potash and soda, and bicarbonate of soda in excess. The 
results M. Lenssen obtained by this method are satisfactory, 

* Mohr : TraiU cf Analyse, pp. 297 and 349. 

t Annalen der Cliemie und Pharmacie , vol. cxiv. p. 114, 


ESTIMATION OF TIN BY MEANS OF A STANDARD SOLUTION. 419 


by using the atomic weight of tin generally adopted (59). 
We shall see farther on why M. Lenssen’s results agree. 

M. Stromeyer* having recently occupied himself with 
the same subject, has succeeded in solving the difficulty. 
The solution of protochloride of tin is carefully introduced 
into an excess of sesquichloride of iron. The salt of iron 
becomes reduced to a minimum according to the following 
equation:— 

Sn + 2(Fe 2 Cl 3 ) = SnCl 2 + 4FeCl. 


It is then estimated by permanganate, as if it were a salt 
of protoxide of iron. The results M. Stromeyer obtains 
in this way are very exact. The author adds that such a 
method of estimating is applicable only in the absence 
of copper or iron, as these two metals decompose per¬ 
manganate of potassa, as well as the tin ; but it may be 
of great use in the estimation of commercial salts of tin. 

M. Scheurer Kestner has endeavoured to determine the 
causes of the variations observed when oxidising a so¬ 
lution of protochloride of tin, proximately by perman¬ 
ganate of potash, and whether, as M. Mohr supposes, these 
anomalies arise only from the presence of oxygen dissolved 
in the water. To make these experiments agree better, the 
solution of protochloride of tin mixed with the proper 
quantity of water has been instantaneously oxidised by per¬ 
manganate, so as not to take time into consideration. The 
irregularities occurring during this operation are shown in 
the following table :— 


c. c. Permanganate. 

2 of Sn Cl, without water, required 34-5 


2 

2 

2 

2 

2 

O 

A 

2 

2 

2 

2 

2 

2 

2 


yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 


and 


yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 


10 c. c. water 
20 


60 

100 

200 

3C0 

400 

600 

600 

700 

800 

900 

1,000 


yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 


yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 

yy 


34-6 
34 6 
34-5 
340 
330 
330 
310 
31-0 
290 
300 
28-5 
28-0 
28-0 


Annalen der Chemie mid Pharmacie, vol. cxvii. p. 261. 

e e 2 



420 


TIIE ASSAY OF TIN. 


c. c. Permanganate. 


2 of Sn Cl and 1,200 o.c. water, required 25 0 


2 

» 

V 

1,400 

it 

ff 

230 

2 

V 

V 

1,000 

if 

ff 

22-5 

2 

)) 

)) 

2,000 

it 

)) 

170 

2 

)) 

)) 

3,000 

it 

)) 

8-0 

2 

)) 

1) 

4,000 

it 


100 

2 

)) 

)) 

5,000 

it 

ft 

170 

2 

)) 

)) 

0,000 

it 

tt 

180 

(A) 2 

V 

V 

8,000 

ff 

» 

24-0 

2 

)} 

)) 

10,000 

it 

tt 

23-0 

2 


)) 

14,000 

it 

tt 

25-0 

2 

)) 

)) 

24,000 

it 

tt 

32-5 

(B) 2 

V 

V 

24,000 

ft 

V 

320 


Leaving A and B to rest for ten minutes,— 

(A) required 14-0 of permanganate. 

(B) „ 25-0 

The result of these experiments is that the more the 
solutions are diluted, the less permanganate is necessary 
until the proportion becomes about 10,000 parts of water 
to one of tin (100 cubic centimetres of the oxidising liquid 
corresponding to one gramme of tin). From this point the 
quantities of permanganate necessary are again augmented, 
and when the dilution is brought to y- 2 o 0 0 th, as much per¬ 
manganate is needed as when it was only at ^L-^th. The 
oxygen of the water then seems to have very little action on 
concentrated solutions, while on diluted solutions its action 
is very marked. At a certain degree of dilution, however, 
these phenomena are reversed, and instead of continuing to 
augment, the sensitiveness of the liquid for oxygen" di¬ 
minishes more and more, becoming gradually reduced to 
what it was in the concentrated solutions. In the preceding 
experiments no account has been taken of time ; the oxida¬ 
tion always took place immediately after the protochloride 
was mixed with water. By allowing the very dilute 
protochloride to remain several minutes before adding the 
permanganate, a much greater absorption of the oxygen 
of water takes place, as shown by the experiments A and B. 

If the oxygen of water is the cause of these variations, 
they ought not to take place when boiled water freed from 
air is used; and in fact they do not then take place. Water 
was boiled, and the temperature then lowered to 80° the 
protochloride was then introduced, and the estimation pro¬ 
ceeded with. The following results show that in operating 




ESTIMATION OF TIN BY MEANS OF A STANDARD SOLUTION. 421 


thus the standard does not vary, whatever quantities of 
water are used. 


Protocliloride 

employed 

Quantities of 
Water 

Standards found 

With 

Cold Water 

With 

Boiled Water 

2 

100 

26 

26 

2 

200 

23 

26 

2 

300 

22 

26 

2 

400 

21 

26 

2 

800 

19 

26 

2 

900 

17 

26 

2 

1,000 

1,200 

16 

26 

2 

13-5 

26 


For studying the action of free oxygen on diluted and 
concentrated solutions of tin, the author passed a current of 
this gas into various solutions of protochloride of tin. For 
this purpose two flasks, communicating by a tube, are filled, 
one with a solution of 2 cubic centimetres of protochloride 
of tin in 100 cubic centimetres of water, and another with 
the same quantity of protochloride in 1,000 cubic centimetres 
of water. The oxygen current, forced to traverse the con¬ 
tents of the first flask before arriving at the contents of the 
second, during an hour, the liquids in the two flasks filtered 
and tested by permanganate of potash, yielded the following 
results:— 

c.c. c.c. 

1st Flask, containing 2 Sn Cl in 100 water, required 25-5 permanganate. 

2nd Flask „ „ 1,000 „ „ 9-2 „ 

2 c. c. Sn Cl, in 1,000 of water, without oxygen current, 16 0 „ 

The first flask contained the strongest solution, and re¬ 
ceived the oxygen first, and absorbed only an amount of 
oxygen represented by 0*5 of permanganate; while the 
metal solution of the second flask absorbed a quantity 
represented by 16 — 9-2 = 6*8 of permanganate. The same 
experiment repeated by employing only 50 cubic centi¬ 
metres of water in the first flask, and by continuing the 
oxygen current for two hours and a half, gave the following 
numbers :— 

1st Flask, containing 50 c. c. of water, 2‘6 permanganate. 

2nd Flask „ 1,000 „ „ 32 „ 

In this case the concentrated solution of protochloride 
of tin did not absorb oxygen, while the diluted solution 
absorbed a quantity equivalent to 16 — 3-2 = 12*8 of per_ 













422 


THE ASSAY OF TIN. 


manganate, that is to say, nearly half the oxygen necessary 
to oxidise the protochloride completely. 

M. Mohr’s experiments prove* that the oxygen of water 
has not the slightest action upon salts of protoxide of iron, 
whilst under the same conditions the protoxide itself oxidises 
immediately. M. Mohr has taken advantage of this property 
to estimate by means of permanganate the oxygen dissolved 
in water. It is interesting then to observe whether there 
exists between protochloride and protoxide of tin a dif¬ 
ference of affinity for oxygen, analogous to that distin¬ 
guishing the salts of iron of the oxide. This analogy, in 
fact, exists, only the reactions are inverse; that is to say, 
protoxide of tin manifests no affinity for free oxygen, while, 
as we have seen above, the protochloride combines more or 
less rapidly with this gas dissolved in water. 

For estimating the oxide of tin by permanganate of 
potash (or, what comes to the same thing, a solution of 
protochloride with the addition of carbonate of soda), M. 
Kestner made use of the ingenious method M. Pean de 
Saint-Giles f employed while studying the oxidising action 
of permanganate in alkaline liquids. This method consists, 
as is well known, in the joint use of permanganate of potash 
and protochloride of iron. 

In making the following experiments a slight excess of 
carbonate of soda was added to the protochloride of tin, 
then an excess of permanganate of potash ; and, lastly, 
ferrous chloride and acid. 

Thus, the following are the standard solutions :_ 


Sn Cl. employed 

| Cubic centimetres 

I 

Quantities of 
water 

Observed 

With the 
protoxide 

Standard 

With the 
protochloride 

2 

400 

14 

14 

2 

600 

14 

14 

2 

600 

14 

12 

2 

700 

14 

10 

2 

1,000 

14 

8 

2 

1,500 

14 

5-6 

2 

2,000 

14 

5 

2 

3,000 

14 

4-2 

2 

3.000 

14 

4 


Trade d 1 Analyses par Liqueurs Titrees, p. 260. 
t Annales de Chimie et de Physique, vol. iv. third series. 




















ESTIMATION OF TIN BY MEANS OF A STANDARD SOLUTION. 423 


The small degree of affinity between oxide of tin and 
oxygen is made evident by passing a current of oxygen 
in a solution of protochloride of tin with carbonate of 
soda in excess. A solution containing 2 cubic centimetres 
of protochloride to 1,000 cubic centimetres of w r ater is 
unaltered, even though a rapid current of oxygen is passed 
through it for two hours. 

The oxygen of water then has no influence on protoxide 
of tin, and the results obtained are very regular, which 
explains why M. Lenssen, by using an alkaline liquid, ar¬ 
rived at corresponding results. 

This property might be of service in estimating the oxygen 
dissolved in water if the oxidation of the protochloride 
w T ere not so slow. It is sometimes necessary to wait very 
long before adding the permanganate, until all the oxygen 
of the water is absorbed, which is always done after some 
time, as may be seen by the following experiments:— 


Water 

1,500 


Permangante Permangante 
required by required by 

the Chloride the Protoxide 
of Iron of Iron 

24 12-5 


Permangante 
required by 
the Protochloride 
of Tin 

After quarter of an hour 
After half an hour 


15 

13 


We have seen that M. Stromeyer, by a happy modifi¬ 
cation, has reduced the estimation of tin to that of iron. 
Applying the same principle, a salt of copper may be 
substituted for a salt of iron. An equivalent quantity of 
copper can thus be estimated in place of tin; and M. Mohr’s 
as well as M. Terrell’s * experiments show that copper can 
be very exactly estimated by permanganate of potash.f 
A double decomposition takes place on protochloride of 
tin being added to nitrate or chloride of copper in excess ; 


* Comptes-Rendus, vol. xlvi. p. 230. 

t For the estimation of copper, variable quantities of water can be used 


Water employed 

0 




Permanganate required by 
a reduced Salt of Copper 

. 16*3 

100 




. 16-4 

16-3 16*4 

500 




. 16-3 


1,000 




. 16-3 


1,500 




. 16-4 

16-3 16*3 

2,000 




. 16-3 


2,500 




. 16-4 

16-3 

3,000 




. 16-4 









424 


THE ASSAY OF TIN. 


a salt of suboxide of copper forms, and the tin passes to 
the maximum state of oxidation, according to the following 
equation:— 

4CuO 2SnCl = 2Cu 2 0 + SnCl 2 + Sn 2 0. 

To estimate-tin, it is, then, sufficient to transform it into 
protochloride, to add to it a solution of nitrate of copper 
slightly in excess, before diluting it with water, and to 
estimate the liquid obtained by permanganate of potash. 

The following experiments show that, whether the opera¬ 
tion is performed with nitrate of copper or whether we 
avail ourselves of oxidation in an alkaline medium, the 
results are the same:— 

10 c. c. SnCl in 1,200 c. c. of water required . 52 of permanganate 

10 „ SnCl in 1,200 c. c. of water, to which is 

added CuO.N0 5 , required ... 87 „ 

10 „ SnCl + Na0C0 2 -t-S0 3 -f-FeCl required . 231 „ 

Deducting that needed for the salt of iron . . 144 „ 

Leaves the remainder ..... 7 the salt of tin. 

1T17 grains of tin, obtained by electrolysis, were dis¬ 
solved in hydrochloric acid and diluted with water suffi¬ 
cient to make the entire volume 200 cubic centimetres. 
30 cubic centimetres of this solution required 9-2 cubic 
centimetres of permanganate, whether the operation was per¬ 
formed with nitrate of copper or with an alkaline solution. 

Permanganate was standardised by means of crystallised 
double sulphate of iron and ammonia, Fe0,S0 3 + NH 4 0, 

so 3 +ho. 

2-918 grains of this salt required 24 cubic centimetres of 
permanganate. The salt containing 14-386 per cent, of 
iron, the 2-918 grammes of it contain 0-416865, or, rather, 
1 cubic centimetre of permanganate = 0-017268 of iron 
corresponding to 0-01818 of tin (59 Sn = 2 * 28 = 56 Fe). 

9-2 cubic centimetres of permanganate were required by 
30 cubic centimetres of the foregoing solution of tin, making 
0-16725 of tin. ° ° 

Thus we have :— 

Tin taken .... 0T6755 
Tin found .... 0T6725 

Difference = 0-00030 




BLOWPIPE REACTIONS OF TIN. 


425 


By calculating the equivalent of tin by these data, and by 
removing the iron from it, we obtain 59-105, which differs 
little from 59-00, the number generally adopted. 

The result of these experiments is, that by passing an 
oxygen current through a concentrated solution of proto¬ 
chloride of tin, the oxygen is not fixed ; in diluted solutions, 
on the contrary, the oxygen is rapidly absorbed by the stan¬ 
nous salt. Oxygen does not act on hydrated protoxide of 
tin. The variations noted in the strength found when pro- 
tochloride of tin is oxidised by permanganate of potash are 
not observed in concentrated solutions ; they take place only 
in presence of oxygen dissolved in water. 

There are then three different processes for estimating tin 
by permanganate of potash :—1. To operate with water freed 
from air by boiling, protecting it from access of air while 
cooling. 2. To oxidise protoxide of tin in an alkaline 
medium. 3. To decompose protochloride of tin either by 
a salt of iron, as proposed by M. Stromeyer, or by a salt of 
copper. 


BLOWPIPE REACTIONS OF TIN. 

Tin deposits an oxide upon charcoal which is feebly yel¬ 
low, and moderately phosphorescent when hot; on cooling 
it is white, and almost touches the assay. It assumes, with 
cobalt solution, a bluish-green colour, which may be readily 
distinguished from that produced by zinc. 

Tin Pyrites .—Tin is readily recognised in this mineral by 
exposing a small piece of it to the oxidising flame on char¬ 
coal. The assay at first exhales a sulphurous acid smell, 
afterwards becomes snow-white on the exterior, and a white 
coating is perceived on the support surrounding the 
specimen : this sublimate is so abundant, that the charcoal is 
not seen in any part between it and the metallic bead. This 
deposit is not expelled in either flame; in other respects, its 
compartment is similar to the oxide of tin. 

The best method for the detection of tin in tantalites and 
tin slags is by reduction with soda; but in such a case it is 
necessary to add a small portion of borax, to dissolve the 


423 


TI1E ASSAY OF TIN. 


tantalic combinations, and prevent the reduction of iron. 
After the completion of the process, the tin is obtained 
by pulverisation and sifting. To be convinced that the 
metallic particles obtained are tin, dissolve protoxide of 
copper in microcosmic salt, add some of them to the flux, 
and then heat the whole upon charcoal in the reducing 
flame. If tin is present, the glass will be coloured reddish 
on cooling. 

Oxides of Tin.— Alone, the protoxide, in the state of 
hydrate, lights and burns like tinder, becoming peroxidised. 
The peroxide does not fuse or undergo any change except 
in the reducing flame, which, if strong and long continued, 
entirely reduces it without the aid of any reagent. Never¬ 
theless, this operation requires much practice and experience. 

With borax it fuses with great difficulty and in small 
quantity, giving rise to a transparent and colourless glass, 
which remains so during cooling. The colour of the glass 
is not changed in the reducing flame. 

With microcosmic salt it behaves as with borax. 

Soda and oxide of tin combine with effervescence on the 
platinum wire. The result of this combination is a blebby 
infusible mass, which cannot be dissolved by a large quantity 
of borax. On charcoal it is easily reduced, and gives a 
grain of tin. 


427 


CHAPTEB XTT 

ASSAY OF ANTIMONY. 

Antimonial substances susceptible of being assayed by the 
dry way are divisible into two classes. 

Class I. In this class are comprised native antimony and 
all antimonial substances containing oxygen or chlorine, 
and but little or no sulphur. 

These substances are the following :— 

Native antimony, Sb, 

Oxide of antimony, Sb 2 0 3 , 

Antimonions acid, Sb 2 0 4 , 

Antimonic acid, Sb 2 0 5 . 

Class II. includes the sulphide of antimony and all anti¬ 
monial ores containing much sulphur. 

Sulphide of antimony, Sb 2 S 3 , 

Oxysulphide of antimony, Sb 2 0 3 -{-2Sb 2 S 3 , 

Haidingerite, 2Sb 2 S 3 + oFeS. 


ASSAY OF ORES OF THE FIRST CLASS, 

All the oxides of antimony are very readily reduced by 
charcoal; so that their assay presents no difficulty. The 
assay is conducted in precisely the same manner as that of 
oxide of lead ; only, as antimony is much more volatile 
than lead, the heat must be managed with care, and the 
assay taken from the fire as soon as finished. When all 
suitable precautions are taken, the loss of antimony is not 
very considerable ; but Berthier says it is never less than 
from 5 to 6 per cent. This, I think, is too high. Thus 
the pure protoxide gives 77 per cent, of metal, and anti- 
monious acid 75. The reduction is readily made, without 
addition, in a charcoal crucible ; but when the substance to 


428 


THE ASSAY OF ANTIMONY. 


be assayed is mingled with impurities, some flux must be 
added. It succeeds equally well with 3 parts of black 
flux, with 1 part of tartar, with 1 part of carbonate of soda, 
and 15 per cent, of charcoal, or any other equivalent re¬ 
ducing flux. * 

When the substance under assay contains oxide of iron, 
the latter oxide is more or less reduced, and the metallic 
iron alloys with the antimony. 

Oxidised matters which contain but a small quantity of 
sulphur can also be assayed in this manner ; because the 
sulphide gives up to black flux the small quantity of anti¬ 
mony which it contains, so that but little remains in the 
slag. The common glass of antimony produces by this 
method of assay 70 per cent, of antimony, and occasionally 
even more than that. 

The ores of this class occur very seldom, and are only in 
rare cases subject to assaying. 


ASSAY OF ORES OF THE SECOND CLASS. 

As pure sulphide of antimony (antimonium crudum) as 
well as metallic antimony (regulus of antimony) are mer¬ 
cantile substances, the assays of the ores of this class have 
for their object the determination of both these bodies. 

I. Determination of the pure Sulphide of Antimony 

(Antimonium Crudum). 

Sulphide of antimony is almost the only mineral from 
which antimonium crudum is produced. This mineral gene¬ 
rally occurs intermixed with very refractory gangue (gneiss, 
quartz, limestone, etc.). Sulphide of antimony fuses readily 
at a low red heat, and is not changed during fusion, if at¬ 
mospheric air is precluded. At a white heat it volatilises 
without change of composition. 

The assay of sulphide of antimony is now effected by a 
liquation process, i.e. by heating the mineral sufficiently in 
order to melt the sulphide of antimony, and, by this means, 
to separate it from the refractory gangue. The production 


DETERMINATION OF REGULUS OF ANTIMONY. 


429 


of sulphide of antimony on a large scale is done in the same 
way. 

For the assaying purpose, two pots or crucibles are used, 
one standing in the other one, and leaving sufficient space 
between the two bottoms to receive the fused sulphide of 
antimony. The bottom of the inside crucible is furnished 
with holes. The mineral to be assayed is put into the 
inside crucible, the latter is then closed with a cover, and 
hermetically luted ; the joints of the two crucibles are also 
luted. The under crucible is then put on the hearth of a 
furnace, enclosed with ashes or sand, in order to keep it 
cool, and the upper crucible, as far as it is outside of the 
under crucible, is covered with coal, and heated to a mode¬ 
rate red heat. The sulphide of antimony will then melt 
and collect in the under crucible, from which it may be 
taken out, after cooling, and weighed. 

2. Determination of Degulus of Antimony. 

This assay may be made in two ways : first, by roasting 
and fusing the oxidised matter with black flux ; secondly, by 
fusing the crude ore with iron, or iron scales, with or with¬ 
out the addition of black flux. 

The roasting of sulphide of antimony requires much care, 
for it is very fusible and volatile, as is also the oxide its 
decomposition gives rise to. The heat ought to be very 
low during the operation, and the substance continually 
stirred. When no more sulphurous acid is given off, we may 
feel assured that it is perfectly roasted, because no sulphate 
is ever formed in this operation. 

The roasted sulphide is then fused with three parts of black 
flux, or its equivalent. 

Metallic iron very readily separates all the sulphur from 
sulphide of antimony; but as sulphide of iron has a 
specific gravity near that of antimony, the separation is very 
difficult to manage : a strong fire must be employed when 
the desulphurisation is complete, to keep the whole body in 
full fusion, for a considerable time With these precautions 
two buttons are obtained, which separate very well: the 


430 


THE ASSAY OF ANTIMONY. 


one white, and in large plates, which is antimony; and the 
other a bronze yellow, a little brighter than the ordinary 
sulphide of iron, because it is mixed with a little metallic 
antimony. During the operation a very considerable portion 
of antimony is always volatilised, which, by this process, is an 
inconvenience impossible to avoid. 

It is, nevertheless, practised in the large way in some 
factories ; but a good result is not generally obtained. It, 
however, appears that when all the necessary precautions 
are taken, it can be employed with advantage. 

The first precaution which is indispensable is, mixing with 
the sulphide only the precise proportion of iron necessary to 
effect its decomposition, which quantity amounts to about 
42 per cent, of its weight. If more be placed, the antimony, 
having a great tendency to play the part of an electro-negative 
element, will combine with the surplus, and an antimonide 
of iron result, part of which will remain in the antimony and 
part in the slag. 

Further, the iron ought to be in the finest possible state 
of division. If the masses be large, a portion of sulphide of 
antimony is volatilised before they can be fully attacked. 
In general, 63 per cent, of antimony can be extracted from 
sulphide by the aid of iron in the small way, but on the 
large scale it seems that 55 per cent, is the maximum. 

Cast-iron cannot be employed instead of wrought, because 
sulphur has very little action in it. The desulphurisation 
is imperfect, and the slag adheres to the reduced metal. 

One of the greatest inconveniences in separating sulphur 
from antimony by means of iron is the strong heat necessary 
to separate the slag from the metal. This might be 
remedied by making the slag more fusible and less heavy, by 
the addition of some flux, as an alkaline carbonate or sulphate. 

If sulphide of antimony be fused with an alkaline car¬ 
bonate and charcoal, regulus is obtained, and a slag com¬ 
posed of an alkaline sulphide and sulphide of antimony. If 
metallic iron be thrown into this slag whilst in fusion, all the 
antimony separates immediately, and a new slag is formed 
as fluid as the former, containing sulphide of iron and sul¬ 
phide of the alkaline base employed. If, instead of the 
above process, the iron be mixed intimately with the sui- 


DETERMINATION OF KEGULUS OF ANTIMONY. 


431 


phide of antimony and carbonated alkali, the result is the 
same—100 parts of sulphide, 42 of metallic iron, 50 of 
carbonate of soda mixed with one-tenth of its weight of 
charcoal, or 50 of black flux : give 65 to 66 of regulus ; with 
the same proportion of iron, and only 10 of flux, only 62 per 
cent, can be obtained. In these two cases the fusion takes 
place very rapidly and without bubbling, and the slag, 
which is very liquid, separates readily from the metal. By 
employing 1 part of alkaline flux, the proportion of iron can 
be reduced from 25 to 30 per cent., and the product of 
metal is always from 65 to 66 per cent. 

Hence, in making an assay of sulphide of antimony, it is 
always better to employ a smaller quantity of iron than is 
necessary to complete the desulphurisation, and make up 
for it by increasing the quantity of flux: then it may be 
insured that no excess of iron will be present. 

The alkaline sulphates are decomposed into alkaline sul¬ 
phides by the agency of charcoal at a slightly elevated 
temperature. The sulphides of the alkaline metals, by com¬ 
bining with the other metallic sulphides, augment their 
fusibility very considerably. Thus when sulphate of soda, 
mixed with about one-fifth of its weight of charcoal, is added 
to a mixture of sulphide of antimony and metallic iron, the 
metallic antimony separates very rapidly, and the slag almost 
instantly becomes perfectly fluid. 

But it must be noted that the presence of an alkaline sul¬ 
phide diminishes the product of regulus, unless the propor¬ 
tion of iron be augmented at the same time. 

For instance, with 

100 parts of sulphide of antimony, 

42 parts of iron, 

100 parts of sulphate of soda, 

20 parts of charcoal, 

but 22 parts of regulus were furnished ; but with 

100 parts of sulphide of antimony, 

42 parts of iron, 

10 parts of sulphate of soda, 

2 parts of charcoal, 

62 parts of antimony were easily obtained. 


432 


TIIE ASSAY OF ANTIMONY. 


Instead of metallic iron, pure oxide of iron may be used, 
or any ferruginous matter whatever, provided it is rich ; but 
it is necessary to add, at the same time, an alkaline flux and 
charcoal to reduce the oxide of iron. 

Not less than 40 parts of iron scales can be employed for 
100 of sulphide of antimony, and then, on the addition of 
50 to 100 parts of carbonate of soda and 8 to 10 of charcoal, 
about 56 of regulus are obtained ; but if with 100 parts of 
carbonate of soda from 14 to 15 parts of charcoal be em¬ 
ployed, 65 parts of antimony are the result. By augmenting 
the proportion of scales, that of soda may be diminished. 
Thus, if from 56 to 60 parts of scales, 10 of soda, and 10 
of charcoal be employed, 50 parts of regulus are the result; 
and if the proportion of soda be 50, and that of carbon 
10, from 65 to 66, and even 67, parts of regulus are 
obtainable. 

The fusion always takes place quickly, and the slags are 
very fluid. 

When sulphide of antimony is fused with forge slag 
(silicate of protoxide of iron), carbonate of soda, and char¬ 
coal, a very white crystalline regulus, in large plates, is 
obtained ; together with a bronze yellow matter, and a black, 
opaque, vitreous slag, shining like jet, in which the greatest 
portion of the alkali employed appeared to be concentrated. 
These three substances separate very readily from each 
other. 

100 parts of sulphide of antimony, 

80 parts of forge slag, 

50 parts of carbonate of soda, 

10 parts of charcoal, 

produced very readily 60 parts of regulus. 

The best method of assaying sulphide of antimony seems 
to be one in which it is mixed with four parts of cyanide 
of potassium, and heated very gently in a crucible. The 
heat required in this case is so low, and the operation is 
made so quickly, that none, if any, of the antimony is lost: 
so that this process is decidedly preferable in the way of an 
assay. In particular cases, however, the wet method must 
be had recourse to. 


DETERMINATION OF REG ULUS OF ANTIMONY. 


4:33 


The sulphide of antimony is analysed by boiling with 
aqua regia. The residue consists of sulphur and gangue. 
It is to be washed and dried, then weighed and ignited. 
The loss will be sulphur, and the remainder is pure 
gangue. 

Water is then added to the filtered solution, which will 
cause the precipitation of some of its contained antimony as 
oxichloride: this must be separated by filtration. The 
solution is then to be saturated with carbonate of potash, 
and a new precipitate will be formed. The solution is to 
be filtered, and made slighly acid ; then nitrate of baryta 
must be added to it to separate its sulphur as sulphate of 
baryta, which it to be washed, dried, and weighed: its 
weight indicates the amount of sulphur: 116 parts are 
equal to 16 parts of sulphur. 

The precipitate by water of oxichloride which remains on 
the filter is redissolved by hydrochloric acid, and its antimony 
separated in the metallic state by means of zinc. The pre¬ 
cipitate formed by carbonate of potash can contain lead, 
copper, iron, and antimony. It must be treated by nitric 
acid, which dissolves everything but the antimony, which 
may then be estimated as antimonic acid. 

It is always best, before conducting the analysis of sul¬ 
phide of antimony, to affuse it with very dilute hydrochloric 
acid, in order to dissolve a portion of the carbonate of lime, 
which may form part of the gangue. As the composition of 
the sulphide of antimony is constant, the following process 
is sufficient in the assay of an antimonial ore :— 

Boil the ore, after treatment with dilute hydrochloric acid, 
with concentrated hydrochloric acid, which dissolves only 
sulphide of antimony, and precipitate the metal as oxichloride 
by means of water. 

Or, after all gangues soluble in dilute hydrochloric acid 
have been removed, the residue may be weighed, and then 
acted on by boiling hydrochloric acid, until all action ceases. 
The residue must be well washed with weak hydrochloric acid, 
dried, ignited, and weighed; the loss of weight corresponds 
to the percentage of pure sulphide of antimony, which con¬ 
tains 72 T per cent, of metal. 


434 


THE ASSAY OF ANTIMONY. 


The following methods of determining antimony are given 
by Mr. Sutton. 

1. Conversion of Oxide of Antimony in Alkaline Solution into 

Antimonic Acid by Iodine {Mohr, residts accurate). 

The oxide of the metal, or any of its compounds, is 
brought into solution as tartrate by tartaric acid and water ; 
the excess of acid neutralised by neutral carbonate of soda, 
then a cold saturated solution of bicarbonate of soda added 
in the proportion of 20 c. c. to about 0T Gm. of Sb0 3 ; to the 
clear solution starch liquor and ^ iodine are added until the 
blue colour appears ; the colour disappears after a little 
time, therefore the first appearance of a permanent blue is 
•accepted as the true measure of iodine required. 

1 c. c. J iodine = O'OOGl Gm Sb. 

2. Distillation of Ter- or Pentasidphide of Antimony with 
Hydrochloric Acid and Titration of the evolved Sul¬ 
phuretted Hydrogen (/ Schneider, results accurate). 

When either of the sulphides of antimony are heated with 
hydrochloric acid in Bunsen’s, Fresenius’, or Mohr’s dis¬ 
tilling apparatus, for every 1 eq. of antimony present as 
sulphide 3 eq. of sulphuretted hydrogen are liberated. If 
therefore the latter be estimated, the quantity of antimony 
is ascertained. The process is best conducted as follows :— 

The antimony to be determined is brought into the form 
of ter or pentasidphide (if precipitated from a hydrochloric 
solution, tartaric acid must be previously added, to prevent 
the precipitate being contaminated with chloride), which, 
together with the filter containing it, is put into the dis¬ 
tilling flask with a tolerable quantity of hydrochloric acid 
not too concentrated. The condensing tube contains a 
mixture of caustic soda, or potash, with a definite quantity 
of f 0 arsenious acid solution, in sufficient excess to absorb 
all the sulphuretted hydrogen evolved. The flask is then 
heated to boiling, and the operation continued till all 
evolution of sulphuretted hydrogen has ceased ; the mixture 


BLOWPIPE REACTIONS OF ANTIMONY. 


435 


is then poured into a beaker, acidified with hydrochloric acid, 
to precipitate all the tersulphide of arsenic. The whole is 
then diluted to, say 300 c. c., and 100 c. c. taken with a 
pipette, neutralised with carbonate of soda, some bicarbonate 
added, and the titration for excess of arsenious acid performed 
with * iodine and starch. 

BLOWPIPE REACTIONS OF ANTIMONY. 

Red and Black Sulphides of Antimony.— Alone, they fuse 
readily on charcoal, which absorbs them and becomes 
covered with a black vitreous crust. After the blast lias 
been continued for a few moments, metallic globules ap¬ 
pear on the charcoal, which seem to be a sub-sulphide, as 
they do not behave like the pure metal ; for they do not 
burn, but blacken, and become dull on the surface after 
cooling. 

Roasted in the glass tube, much antimonious acid forms 
at the commencement; that which sublimes afterwards is a 
mixture of antimonious acid with much oxide. 

Antimony and its Oxides.— Metallic antimony fuses readily 
on charcoal, and, when heated to redness, remains a consi¬ 
derable time in a state of ignition without the aid of the 
blowpipe, disengaging a thick white smoke. This smoke is 
gradually deposited on the charcoal around the metallic 
globule in small crystals, having a pearly lustre, and which, 
in course of time, cover it entirely. These crystals are 
oxide of antimony. Metallic antimony alone in the matrass 
does not sublime but at the fusing point of glass. Heated 
to redness in the open tube, it burns slowly, giving a white 
smoke, which deposits on the glass, and presenting here and 
there traces of crystallisation. 

Oxide of Antimony. — Alone , readily fuses, and passes off 
as a thick white vapour. It is reduced to the metallic 
state on charcoal. In this operation it colours the flame 
greenish. 

Antimonious Acid does not fuse, but gives off a vivid 
licrht, diminishing; at the same time in bulk, and covering 
the charcoal with a white powder, but is not reduced. 

r f 2 


436 


TI1E ASSAY OF ANTIMONY. 


Antimonic Acid whitens at the first impingement of the 
flame, and is converted into antimonious acid. 

The oxides and acids of antimony behave alike with fluxes. 

Borax dissolves a large quantity of antimonious acid 
without becoming opaque. The glass continues yellow while 
hot, but loses nearly all its colour on cooling. When satu¬ 
rated, a portion of the antimony sublimes in the metallic 
state. 

Microscomic salt forms with the same acid a transparent 
and colourless glass. On the platinum wire, in the oxidating 
flame, it becomes yellow, which tint vanishes on cooling. 

With soda ,, on the platinum wire, it fuses into a trans¬ 
parent and colourless glass, which becomes white on cooling. 
It is reduced on charcoal. 


437 


CHAPTER XIII. 

THE ASSAY OF ZINC. 

All bodies containing zinc, usually found in the assay 
office, may be divided into four classes :— 

Class I.—Zinc ores, in which the metal exists as oxide 
not combined with silica :— 

Earthy oxide of zinc, ZnO. 

Manganiferous oxide of zinc, brucite, ZnO + (MnO) n . 

Aluminate of zinc, Gahnite, Zn0,6Al 2 0 3 . 

Franklinite, 3(FeO,ZnO) + (Fe 2 0 3 ,Mn 2 0 3 ). 

Anhydrous carbonate of zinc, ZnO,CO 2 . 

Hydrated carbonate of zinc, ZnO,3HO+ 3Zn0,C0 2 . 

Class II.—Zinc ores, in which the metal exists, as in the 
former class, as oxide, but partly or wholly combined with 
silica:— 

Anhydrous silicate of zinc. 

Hydrated silicate of zinc, electric calamine, Zn0, 2 Si0 3 + ZnO,HO. 

Class III.—Zinc ores, in which the metal is partly or 
wholly combined with sulphur:— 

Sulphide of zinc (blende, Black Jack), ZnS. 

Oxysulphide of zinc. (This is rare.) 

Sulphate of zinc, Zn0,S0 3 ,7H0. 

Selenide of zinc, ZnSe. (Very rare.) j 


Class IV.—Alloys. 


ASSAY OF ORES OF THE FIRST CLASS. 

In order to reduce the oxide of zinc contained in sub¬ 
stances of this class, it is sufficient to mix them with charcoal 
and expose them to a white heat. 



438 


TIIE ASSAY OF ZINC. 


At the moment of reduction the zinc is in a vaporised 
state. Its vapours, however, are readily condensible, so 
that the operation may be conducted in an ordinary retort, 
and all the metal is deposited in the neck without the 
slightest loss. It seems from this that nothing is so easy, 
at first sight, as the assay of an oxide of zinc; but it is not 
so. It is very easy to reduce all the oxide, but it is not so 
easy to collect all the zinc ; nor is it easy to condense it all 
in the metallic state, and in consequence to determine the 
precise proportion in the ore submitted to assay. 

This difficulty consists, firstly, in the deposit being ex¬ 
tended over a large surface, and it often adheres very 
strongly to the sides of the retort, so that it is nearly im¬ 
possible to detach it*, and secondly, as the neck of the 
retort is open, the air having access to it, brings to the state 
of oxide all the vapour nearest the end of the neck. The 
proportion of zinc oxidised is larger in proportion to the 
smallness of the quantity submitted to assay, and is always 
very considerable where no more than 200 to 400 grains 
are operated upon. 

It is not, therefore, in the extraction of the zinc from its 
oxide that the assay is rendered partially uncertain, but in 
its collection. 

The distillation of zinc requires a very high temperature, 
and cannot be performed in retorts of glass; those of 
earthenware must be employed. It is not necessary to 
lute these retorts when they are of good quality ; and they 
are better thin, because they heat more rapidly, and are 
not so likely to crack. 

After the mixture of oxide and charcoal has been intro¬ 
duced into the retort, it is placed in the fire. The neck 
ought to have adapted to it a long tube of glass, with a 
narrow bore, so as to collect all the zinc which may escape 
from the wide part of the neck of the retort. This dis¬ 
position is also convenient, as it does not allow such a free 
access of air. 

It is heated gradually until it is white inside; the zinc 
is reduced and volatilised, and condensed in the neck : the 
greater the heat, the nearer the orifice. The metal can be 


ASSAY OF ORES OF THE FIRST CLASS. 


459 


detached readily from the neck, if it be well black-leaded 
inside. It is necessary, from time to time, to observe the 
state of the neck, because when very narrow it is often 
obstructed, and, if not cleaned out with an iron rod, might 
cause an explosion. 

When the operation is finished the apparatus is allowed 
to cool, the retort taken out, placed carefully on its side, 
and broken, in order that if any particles of zinc have con¬ 
densed in its dome, they may be removed. 

* If the approximate proportion of metallic zinc alone be 
the end, all is collected and fused at a very gentle heat in 
a crucible with some black flux ; but if the true quantity of 
zinc is to be estimated it must be done in a more exact 
manner. The deposit must be collected with all possible 
care ; the neck must then be broken to pieces, and every 
piece having adhering to it either zinc or oxide must be 
placed on one side, and digested in hot nitric acid, which 
takes up those substances. If any be put in the glass tube, it 
must be carefully cleaned by means of acid, and the solution 
added to that produced by the digestion of the broken 
neck, and the deposit mechanically collected, in nitric acid. 
The solution is then evaporated gradually to dryness, and 
heated to redness. The nitrate, by these means, is decom¬ 
posed, and transformed into oxide, four-fifths of the weight 
of which is equal to the quantity of metallic, zinc produced 
in the assay. 

The foregoing is the method of estimation by distillation; 
the following is the method of estimation by difference. 
Two plans of assay in this manner may be adopted: firstly, 
at an ordinary assay temperature ; secondly, at a very high 
temperature, as that of an iron assay. In all cases it is 
necessary to commence with the expulsion of all volatile 
bodies the ore may contain. If water or carbonic acid 
alone be present, simple calcination will do; but if car¬ 
bonaceous matter, roasting must be had recourse to. 

When the assay is made at an ordinary assay tempera¬ 
ture, the sample is finely pulverised, and mixed with from 
15 to 20 per cent, of equally finely pulverised charcoal, and 
pressed into a crucible, on which is placed a cover, but not 


440 


THE ASSAY OF ZIXC. 


luted, and rapidly heated to whiteness. When no more 
zinc vapour is disengaged it is cooled, and the mixture in 
the pot collected. The residue ought to be pulverulent; 
but as it is mixed with some charcoal, it is roasted, and 
then weighed. It is evident that the loss represents the 
oxide of zinc : the charcoal added, it is true, leaves a 
small quantity of ash, but it is too small to be accounted 
for. 

In making the assay in the manner described, it is to be 
feared that a small quantity of the oxide remains undecom- 
posed, and that a part of the residue might adhere to the 
crucible, and could not be detached; and lastly, there is 
always a degree of uncertainty in the state of oxidation 
the iron the substance may contain will exist in it after 
roasting. No inconvenience of this nature presents itself 
when the assay is made at a very high temperature. This 
mode is the most exact of all, and leaves nothing to be 
desired. 

The assays of zinc at a high temperature are made 
exactly as those of iron. They are made in a charcoal 
crucible, with the addition of fixed fluxes, suitable to effect 
the fusion of the gangues mixed with the oxide of zinc, if 
they be not fusible by themselves. The button is weighed ; 
it is a compound of slag and grains of iron, which are 
collected and their weight ascertained, and, by the difference, 
that of the slag. The weight of oxj^gen which the iron has 
lost during its reduction is then added to it, and by de¬ 
ducting from the substance the weight of the button and 
the oxygen so obtained, we have the proportion of oxide of 
zinc reduced in the assay. On the other hand, by deducting 
from the weight of the slag the weight of flux added, the 
weight of earthy substances and irreducible oxides which 
were mixed with the oxide of zinc is ascertained. 

These results can be shown in a tabular form, in the 
following manner : — 

Let m be the weight of the crude ore, n the weight 
of the calcined ore, r the weight of the flux added, / the 
weight of the cast-iron, 5 the weight of the slag, 0 the 
weight of oxygen combined with the iron, calculated from 


ASSAYING ORES OF THE FIRST CLASS IN TIIE WET WAY. 441 


the weight of metal produced, z the weight of the oxide of 
zinc, then :— 


i 


m crude ore=calcined ore . . . n 

r fixed fluxes.. 


Gives metal 
Gives slag- . 


Flux added 


nA-r 


\\ Total f+s | j. 

J Oxygen o J 

Oxide of zinc w4 -r — f— s-o 
___ »* 


r 


Earthy matter . . s — r 



The following is an actual experiment by Berthier:— 


100 crude ore=calcined ore 
10 kaolin (china clay) acted on by acids . 
7 marble=lime . 


Gave metal 
Gave slag 


45*31 
16*3 J 


Total . 
Oxygen 

%t C/ 


61*3 

19-4 


} 


Total 


83-3 

100 

40 

97-3 
. 80-7 


Oxide of zinc . 16-6 


Fluxes added.14-0 

Earthy matters . . . . . .2-0 


The above result was confirmed by humid analysis, show¬ 
ing at once the exactitude of the process. 

Determination of amount of Zinc by the Humid Process, 
in Ores of the First Class. —Dissolve 50 grains of the finely 
pulverised ore in nitric acid, evaporate to dryness, allow to 
cool. Digest the cold mass with a little dilute nitric acid, 
gently warming during the digestion, add water, and then 
filter. To the filtered solution add excess of caustic am¬ 
monia, gently warm, and filter. The excess of caustic am¬ 
monia dissolves the oxide of zinc which it at first threw 
down, as well as any oxide of manganese that may be 
present. This solution containing the zinc, and probably 
manganese, must be separated from the precipitate produced 
by the ammonia by filtration, the insoluble matter in the 
filter washed with water containing a little ammonia, and 
the washings so obtained added to the first strong filtrate. 
If no manganese be present, sulphide of ammonium may be 
now added to the filtered liquid until it produces no further 
white precipitate of oxide of zinc. The liquid and precipi¬ 
tate must now be allowed to stand in a warm place for 
about an hour, then filtered, and the sulphide of zinc on the 







412 


TIIE ASSAY OF ZINC. 


filter washed with water containing a little sulphide of am¬ 
monium. After a few washings, it is to be dissolved in 
dilute hydrochloric acid, and, if necessary, the solution 
filtered. To the filtered solution is added excess of car¬ 
bonate of soda: carbonate of zinc is thrown down, which 
in its turn is collected on a filter, washed, dried, separated 
from the filter, ignited, and weighed. Four-fifths of its 
weight is metallic zinc. If by previous experiment by 
blowpipe, or otherwise, manganese were found to be present, 
the ammoniacal solution containing the mixed oxides must 
be thus treated:—Excess of acetic acid is to be added to it, 
and a stream of sulphuretted hydrogen gas passed through 
it until no further precipitation takes place; by this means 
the whole of the zinc is deposited as sulphide, whilst the 
manganese remains untouched in the liquid. The sulphide 
of zinc is to be collected on a filter and treated with hydro¬ 
chloric acid, &c., as just described. 

ASSAY OF ORES OF THE SECOND CLASS. 

The silicates of zinc are not reducible by charcoal alone; 
but when in contact with substances which have the pro¬ 
perty of combining with silica, they are reduced completely, 
even at a moderate temperature. All the modes of assay 
just described for ores of the first class apply to those of the 
second, with the exception that the flux, instead of being 
merely reducing, must have a true fluxing property also: 
lime or magnesia are good fluxes. 

Humid determination of Zinc in Ores of the Second Class. 
—Ores of this class are best decomposed by strong hydro¬ 
chloric acid with a small admixture of nitric acid. When 
thoroughly decomposed, and the solution evaporated to 
dryness, it is moistened with hydrochloric acid, and treated 
exactly as described for Ores of the First Class. 

ASSAY OF ORES OF THE THIRD CLASS. 

In order to assay the substances containing sulphur 
which belong to this class, they must be roasted, and then 



ASSAY OF ORES OF THE THIRD CLASS. 


443 


treated as the ores of the first and second class. Sulphide 
of zinc may be roasted without difficulty; and when the 
operation is made with care, the roasted ore contains neither 
sulphur nor sulphuric acid. The only precaution necessary 
to observe is, that the heat must be carefully regulated at 
first, in order to avoid fusion which might take place, espe¬ 
cially when a certain amount of sulphide of iron is present. 
Towards the end the heat may be increased, to decompose 
any sulphate that may be formed. Both a reducing and 
fusing substance must be added in this case, as in the last, 
in order to determine the fusion of the gangue. 

Humid Determination of Zinc in Ores of the Third 
Class .—These ores are to be finely pulverised, treated with 
strong nitric acid, at first with a gentle heat; and lastly, 
boiled until the sulphur separates in bright yellow trans¬ 
parent globules, as described under the Humid Assay of 
Copper Ores of the Second Class. The solution so obtained 
is to be evaporated to dryness, moistened with hydro¬ 
chloric acid, and treated as described for ores of the first 
class. 

If ores of this class, or of either of the two former, con¬ 
tain copper, they must be thus treated :— 

The ore is to be decomposed by an appropriate acid, 
evaporated to dryness, moistened with hydrochloric acid, 
water added, and the solution filtered. A current of sulphu¬ 
retted hydrogen gas is now to be passed through the solu¬ 
tion until, even after violent agitation, it smells strongly of 
it. It is now to be filtered, and the black precipitate on 
the filter contains all the copper as sulphide of copper, that 
substance being insoluble in dilute acid, whilst in a solution 
acidulated with either of the strong mineral acids—as nitric, 
hydrochloric, or sulphuric—zinc is not at all acted on by 
sulphuretted hydrogen. The solution, now freed from 
copper, is placed in an evaporating basin and boiled for 
about a quarter of an hour: nitric acid is then added to 
peroxidise all the iron present, and the solution allowed to 
cool. When cold, the zinc is separated by means of 
ammonia, and the ammonical solution treated as already 
described. 


444 


THE ASSAY OF ZINC. 

FOURTH CLASS. ALLOYS. 

The alloys of zinc with iron, copper, and tin, may be 
assayed by heating them to whiteness for about an hour in 
a charcoal crucible witli an earthy flux (silicate of lime is 
the best), and weighing the resulting button : the loss will 
be nearly equivalent to the quantity of zinc present. 

The Hamid Determination of Zinc in Substances of the 
Fourth Class .—These substances are treated precisely as de¬ 
scribed under the heads Humid Determination of Zinc in 
First, Second, and Third Classes. 

VOLUMETRIC DETERMINATION OF ZINC. 

Fresenius * gives the following methods for the volumetric 
determination of zinc. 

Several methods have been proposed for the volumetric 
determination of zinc. The most suitable method for tech¬ 
nical purposes f seems to be that based on the precipitation 
of an ammoniacal solution with standard sulphide of sodium. 

This method was originally proposed by ShafFner: it has 
been the subject of a variety of modifications. After this 
method, with its modifications, have been detailed, I shall 
proceed to describe the method of H. Schwarz, and then 
that of Carl Mohr. The two first methods require the zinc 
in ammoniacal solution, while for the last method an acetic 
acid solution is employed. 

1. Method of Schaffner4 modified by C. Kunzel.§ as em¬ 
ployed in the Belgian Zinc-works; described by C. G-roll.|| 

a. Solution of the Ore and Preparation of the Ammoniacal 

Solution. 

Powder and dry the ore. 

Take 0-5 grm. in the case of rich ores, 1 grm. in the case 
of poor ores, transfer to a small flask, dissolve in hydro- 

* 4th English edition, p. 653, published by Churchill and Sons. 

t It is very extensively employed in zinc works. 

| Journ. f. prakt. Chem. 73, 410. 

§ Ibid. 88, 486. 

|| Zeitschrift f. anal. Chem. 1, 21. 


VOLUMETRIC DETERMINATION OF ZINC. 


445 


chloric acid with addition of some nitric acid by the aid of 
heat, expel the excess of acid by evaporation, add some 
water, and then excess of ammonia. Filter into a beaker, 
and wash the residue with lukewarm water and ammonia, 
till sulphide of ammonium ceases to produce a white tur¬ 
bidity in the washings. The oxide of zinc remaining in the 
hydrated sesquioxide of iron is disregarded. Its quantity, 
according to Groll, does not exceed O’3—0*5 per cent. 
This statement probably has reference only to ores contain¬ 
ing relatively little iron; where much iron is present the 
quantity of zinc left behind in the precipitate may be not 
inconsiderable. The error thus arising may be greatly 
diminished by dissolving the slightly washed iron precipitate 
in hydrochloric acid, and adding excess of ammonia. But 
the surer mode of proceeding is to add to the original solu¬ 
tion—after evaporating off the greater part of the free acid 
as above, and allowing to cool—dilute carbonate of soda 
nearly to neutralisation, then to precipitate the sesquioxide 
of iron with acetate of soda, boiling to filter, and wash. The 
washings, after being concentrated by evaporation, are 
added to the filtrate, and the whole is then mixed with am¬ 
monia, till the first-formed precipitate is redissolved. 

If the ore contains manganese—provided approximate 
results will suffice—digest the solution of the ore in acids, 
after the addition of excess of ammonia and water, at 
a gentle heat, for a long time, and then filter off, with the 
iron precipitate, the hydrated protosesquioxide of manganese 
which has separated from the action of the air. The safer 
course—though undoubtedly less simple—is, after separating 
the iron with acetate of soda, to precipitate the manganese 
by passing chlorine, or by adding bromine and heating. 

If lead is present, it is separated by evaporating the aqua 
regia solution with sulphuric acid, taking up the residue 
with water and filtering; then proceed as directed. * 


* Concerning the direct treatment of roasted zinc ores with a mixture of 
carbonated and caustic ammonia, comp. E. Sclimidt ( Jotirn. f. prakl. Client. 
51, 257). By this treatment the oxide of zinc, which was combined with 
carbonic acid, is dissolved, whilst that combined with silicic acid is for the 
most part left undissolved. 




416 


THE ASSAY OF ZINC. 


b. Preparation and Standardising of the Sulphide of Sodium 

Solution . 

The solution of sulphide of sodium is prepared either by 
dissolving crystallised sulphide of sodium in water (about 
100 grm. to 1,000—1,200 water), or by supersaturating 
a solution of soda, free from carbonic acid, with sulphuretted 
hydrogen, and subsequently heating the solution in a flask 
to expel the excess of sulphuretted hydrogen. Whichever 
way it is prepared, the solution is afterwards diluted, so that 
1 c. c. may precipitate about 0*01 grm. zinc. Prepare 
a solution of zinc, by dissolving 10 grm. chemically pure 
zinc in hydrochloric acid, or 44T22 grm. dry crystallised 
sulphate of potash of zinc in water, or 68T33 grm. dry crys¬ 
tallised sulphate of potash and zinc in water, and making 
the solution in either case up to 1 litre with water. 

Each c. c. of this solution corresponds to 0-01 grm. 
zinc. Now measure off 30—50 c. c. of this zinc solution 
into a beaker, add ammonia till the precipitate is redissolved, 
and then 400—500 c. c. distilled water. Pun in sulphide 
of sodium as long as a distinct precipitate continues to be 
formed, then stir briskly, remove a drop of the fluid on the 
end of a rod to a porcelain plate, spread it out so that it 
may cover a somewhat large surface, and place in the middle 
a drop of pure dilute solution of chloride of nickel. If the 
edge of the drop of nickel solution remains blue or green, 
proceed with the addition of sulphide of sodium, testing from 
time to time, till at last a blackish grey coloration appears 
surrounding the nickel solution. The reaction is now com¬ 
pleted, the whole of the zinc is precipitated, and a slight 
excess of sulphide of sodium has been added. The precise 
depth of colour of the nickel must be observed and re¬ 
membered, as it will have to serve as the stopping signal in 
future experiments. To make sure that the zinc is really 
quite precipitated, you may add a few tenths of a c. c. more 
of the reagent, and test again ; of course the colour of the 
nickel drop must be darker. Note the number of c. c. used, 
and repeat the experiment, running in at once the necessary 
quantity of the reagent less 1 c. c., and then adding 0*2 c. c. 



VOLUMETRIC DETERMINATION OF ZINC. 


447 


at a time, till the end reaction is reached. The last experi¬ 
ment is considered the more correct one. The sulphide of 
sodium solution must be restandardised before each new 
series of analyses—that is, if it is kept in bottles containing 
air; if, on the contrary, oxygen is excluded by passing the 
air through an alkaline solution of pyrogallic acid previous 
to its entering the bottle, the solution would without doubt 
keep unaltered. 

c. Determination of the Zinc in the Solution of the Ore . 

Proceed in the same way with the ammoniacal solution 
prepared in a as with the known zinc solution in h. Here 
also repeat the experiment, the second time running in at 
once the required number of c. c., less 1, of sulphide of 
sodium, and then adding 0*2 c. c. at a time, till the end-re¬ 
action makes its appearance. The second result is considered 
the true one. There are three different ways in which this 
repetition of the experiment may be made. You may either 
weigh out at the first two portions of the zinc ore, or you 
may weigh out double the quantity required for one experi¬ 
ment, make the ammoniacal solution up to 1 litre, and em¬ 
ploy i litre for each experiment, or lastly, having reached 
the end-reaction in the first experiment, you may add 1 c. c. 
of the known zinc solution, which will destroy the excess of 
sulphide of sodium, and then run in sulphide of sodium in 
portions of 0*2 c. c. till the end-reaction is again attained. 
Of course, in this last process to obtain the second residt, 
you deduct from the whole quantity of sulphide of sodium 
used the amount of the same, corresponding to 1 c. c. of the 
zinc solution. 

If the ore contains copper, which frequently occurs in the 
case of blendes, determine by a preliminary experiment the 
number of c. c. of sulphide of sodium which are necessary 
to precipitate the copper, and at the completion of the zinc- 
analysis deduct them. In this case, let the drop to be tested 
with nickel solution pass through a small filter on its way to 
the porcelain plate, in order to avoid the injurious influence 
of the sulphide of copper on the nickel reaction. If, how- 


44S 


THE ASSAY OF ZINC. 


ever, the copper amounts to more than 2 per cent., remove 
it from the acid solution by sulphuretted hydrogen, evapo¬ 
rate the filtrate with nitric acid, dilute, treat with ammonia, 
and determine the zinc as above. 

In careful hands the error will, according to C. Kunzel, 
never exceed ^ per cent. 

cl. Further Modification of the Process. 

To ascertain the point when the whole of the zinc is pre¬ 
cipitated and the sulphide of sodium begins to predominate, 
SchafFner * employed flocks of hydrated sesquioxide of iron, 
which he produced by the addition of a few drops of sesqui- 
chloride of iron to the ammoniacal zinc solution, and which 
settled at the bottom ; while Barreswil f used small pieces 
of white porcelain, which were covered with sesquichloride 
of iron, and thrown into the ammoniacal zinc solution. 
Sulphide of sodium is added till the flocks or the pieces of 
porcelain turn black. In neither case is the end-reaction so 
exact as with nickel solution. 

With the help of lead-paper, however, the point may be 
hit with great precision. Moisten a piece of white filter- 
paper with solution of acetate of lead, place it on a layer of 
blotting-paper, drop some carbonate of ammonia upon it, so 
as to form a thin coating of carbonate of lead, let the blot¬ 
ting-paper absorb the excess of moisture, and then spread 
the lead-paper on a porcelain plate. As soon as you imagine 
the zinc to be nearly all precipitated, lay a small piece of 
filter-paper on the lead-paper, and then dip the end of a 
blunt glass rod in the fluid, and press it somewhat gently on 
the small piece of filter-paper. When the sulphide of 
sodium begins to be in excess, a brown spot forms on the 
lead-paper. This lead-paper appears to be more sensitive 
than the nitroprusside of sodium-paper proposed by Carl 
Mohr,J which, however, is very serviceable. Fr. Mohr§ 
applies the lead-reaction in another manner. He makes an 
alkaline solution of lead by warming together acetate of lead, 

* Journ. f. prakt. Chem. 73, 410. 

t Journ. de pharm. 1857, 431 ; Polyt. Centralbl. 1858, 285. 

t Dingler’s Polyt. Journ. 148, 115. 

§ Mohrs Lehrbuck der Titrirmethode, 2 Aufl. 377. 


VOLUMETRIC DETERMINATION OF ZINC. 


449 


Rochelle salt and solution of soda; he first places a drop of 
this on filter-paper, and then close by a drop of the precipi¬ 
tated zinc solution, so that the circle formed by the spread¬ 
ing of the solution to be tested may cut the circle of the lead 
solution. As soon as the sulphide of sodium begins to pre¬ 
dominate, the portion of the circumference of the lead circle, 
which lies in the other circle, turns black. 

2. H. Schwarz’s Method.* 

Prepare an ammoniacal solution as in 1, a. 

Heat gently, and mix with a moderate excess of sulphide 
of ammonium. Allow the precipitated sulphide of zinc to 
subside, then filter, using a tolerably large plaited filter of 
rapidly filtering paper, moistened with boiling water, and 
warming the fluid to accelerate the operation, which would 
otherwise require considerable time. Wash the precipitate 
with warm water mixed with a little ammonia, until the last 
drops no longer blacken a solution of oxide of lead in soda. • 

Transfer the filter with the precipitate to a beaker, add a 
dilute solution of slightly acidified sesquichloride of iron, 
cover with a close-fitting glass plate, and let the mixture 
stand for ten minutes ; then heat gently. Under these cir¬ 
cumstances the sulphide of zinc decomposes completely with 
the sesquichloride of iron to chloride of zinc, protochloride 
of iron, and sulphur : Fe 2 Cl 3 + Zn S = Zn C1 + S + 2FeCl. 

How add sulphuric acid, and heat gently until the sulphur 
has agglutinated. Filter, wash the filter, and determine the 
iron in the fluid as protochloride by permanganate,f 2 eq. 
iron correspond to 1 eq. zinc. If the quantity of sulphide 
of zinc is not very great, the filter may be broken, and the 
sulphide of zinc washed into a flask which already contains 
the solution of sesquichloride of iron. The great objection 
to this method lies in the washing of the sulphide of zinc, 
which, as is well known, is a long and troublesome opera- 

* See Lis Anleitung- zu Maassanalysen, Nachtrage, p. 29 (Brunswick). Coni' 
pare also v. Gellliorn (Chem. Centralbl. 1853, 291), who has made many 
analyses by Schwarz's method. 

t Without doubt the sesquichloride of iron might be replaced by the 
sesquisulphate, by which means the presence of hydrochloric acid would be 
avoided. 


430 


THE ASSAY OF ZINC. 


tion. A possible loss of sulphuretted hydrogen on mixing 
the sulphide of zinc with sesquichloride of iron may be pre¬ 
vented by conducting the decomposition in a flask, connected 
with a U-tube containing sesquichloride of iron. 


3. Carl Mohr’s Method* 

This method is based upon the following considera¬ 
tions :— 

I. If a solution of acetate of zinc, acidified with aCetic 
acid, is mixed with an excess of ferricyanide of potassium, 
the whole of the zinc is thrown down in the form of a red¬ 
dish yellow precipitate of ferricyanide of zinc Zn 3 (Cy 6 Fe 2 ). 

II. If solution of iodide of potassium is now added in ex¬ 
cess, we have this decomposition :—2[Zn 2 (Cy 6 Fe 2 )] + 2KI + 
2(A, HO) = 3[Zn 2 (Cy.Fe)] + 2(KO,A) + H 2 (Cy 8 Fe) + 21. 

III. I eq. liberated iodine corresponds, accordingly, to 
3 eq. zinc. 

IV. If iodide of potassium is made to act upon ferricyanide 
of zinc in a neutral fluid the liberated iodine acts upon the 
ferrocyanide of potassium present in that case, which leads 
to the formation of a little ferricyanide of potassium ; the 
remaining free iodine, therefore, will not indicate, with 
accuracy, the quantity of zinc present. But whereas the 
reaction actually takes place in acid solution of acetate of 
zinc, as above directed, it may be assumed that acetate of 
potassa and free hydroferrocyanic acid are formed ; and as 
iodine exercises no appreciable action upon the latter sub¬ 
stance, the iodine liberated in the process indicates, with 
tolerable accuracy, the amount of zinc present. 

The process is as follows :— 

Treat the ore with aqua regia, as in 1, a, and drive oft' the 
greater part of the free acid ; nearly neutralise with carbo¬ 
nate of soda, add acetate of soda in excess, boil, filter, and 
wash with boiling water mixed with a little acetate of soda. 
The solution is iron-free ; it contains the whole of the zinc, 
but, in presence of manganese, also the whole of the latter 


* Dingler’s Polyt. Journ. 148, 115. 



BLOWPIPE BE ACT IONS OP ZINC. 


451 


metal. Hence the process is not applicable in the presence 
of manganese. 

Mix the solution of zinc, prepared as directed, with ferri- 
cyanide of potassium in slight excess, i.e. until a sample of 
the clear supernatant fluid gives a blue precipitate with a 
salt of protoxide of iron. Then add a sufficient quantity of 
iodide of potassium. The fluid acquires a brown colour, in 
consequence of the liberation of iodine ; the white precipi¬ 
tate of ferrocyanide of zinc is suspended in the brown fluid. 

Determine now the free iodine by means of hyposulphite 
of soda, and calculate 3 eq. zinc for each eq. iodine. The 
results obtained by C. Mohr are very satisfactory. The 
method can be employed only if the acetic acid solution con¬ 
tains no other heavy metal besides zinc, and, more particu¬ 
larly, no manganese. 


BLOWPIPE REACTIONS OF ZINC. 

Zinc Blende, Black Jack, Sulphide of Zinc. — Alone , 
decrepitates violently. Suffers no remarkable change on 
ignition ; does not fuse, and gives off but a very slight 
odour of sulphurous acid, being very difficult to roast. 

On charcoal , an annular deposit of oxide of zinc is 
formed when heated violently in the outer flame. 

Soda attacks it feebly ; but the zinc is reduced in a good 
fire, with the deposition of oxide of zinc on the charcoal. 

Carbonate of Zinc, Calamine.— Alone , gives off no water, 
but becomes a white enamel, which behaves like oxide of 
zinc. 

Oxide of Zinc. — Alone , becomes deep yellow when heated. 
This assay must be made by daylight. It reassumes its 
white colour on cooling. It does not fuse, but gives off a 
vivid light during incandescence. It is gradually evaporated 
in the reducing flame, during the continuance of which a 
yellow ring is deposited on the charcoal, which becomes 
white on cooling. 

o 

With borax it fuses readily, and gives a transparent glass, 
which, with a large proportion of oxide, becomes milky by 
flaming. It assumes an enamel-white appearance on cool- 


G G 2 



452 


THE ASSAY OF ZINC. 


ing. In the reducing flame the metal sublimes, and covers 
the charcoal with a white film. 

With microcosmic salt it behaves as with borax, except 
that the metal sublimes less readily with the first than the 
second. 

Soda does not dissolve it; but acted on by this reagent 
on charcoal, it is reduced, and covers the charcoal with a 
coating of oxide. 


453 


CHAPTER XIV. 

ASSAY OF MERCURY. 

Mercury is found in the native or metallic state, and as sul¬ 
phide or cinnabar :— 

Native mercury, Hg. 

Sulphide of mercury, cinnabar, Hg 2 S. 

Bituminous sulphide of mercury. 

There are other minerals of mercury met with, but 
hitherto not in sufficient quantity to be worked for the 
metal. They are :— 

Zinciferous subsulphide of mercury. 

Zinciferous sulphide of mercury. 

Selenide of mercury. 

Subchloride of mercury. 

Iodide of mercury. 

Silver amalgam \see Silver). 

Assay of Mercurial Ores .—The determination of mercury 
is always made by distillation. In case the mercury is 
present in the form of native mercury, or oxide of mercury, 
it is distilled without any addition. The ore (say from 500 
to 1,000 grains) is placed in an iron or earthenware retort, 
which is set over a suitable fire, and the heat raised gradu¬ 
ally, and kept up, until the whole of the mercury has passed 
over. The mercury which passes over is collected either in 
the neck of the retort, or a receiver fitted for that purpose— 
such as a glass flask kept cool by affusion with water. 
When but a small quantity is operated upon (say 150 to 200 
grains), it is most convenient to use a glass retort, or bent 
tube retort, heating it gradually over a charcoal fire, taking 
care to keep the upper part so hot, that no metallic mercury 



454 


THE ASSAY OF MERCURY. 


may adhere to it. It must be heated nearly to the melting 
point of the glass, and until all the mercury has come over. 

When the operation is finished, the neck is cut off’, 
weighed, the mercury detached, and weighed again: the 
loss of weight is the amount of mercury. Or the metal may 
be detached by means of a feather, and allowed to fall into 
a basin of water, which, if heated for a few seconds, will 
cause the mercury to collect into one globule: the water 
may be decanted, and the mercury dried at the ordinary 
temperature, and weighed. 

The mercury wholly condenses in the neck of the retort, 
under the form of a metallic dew. Some may by chance 
pass off; but in order to prevent such an occurrence, the 
beak of the retort is plunged into water, or a small dossil 
of linen, moistened with water, introduced into the neck, 
the end of which is plunged into water, by which means 
the neck of the retort is kept constantly cool, and the mer¬ 
cury is found deposited on the linen, from which it may be 
detached by shaking in water. 

When large quantities of substances containing mercury 
are operated upon, it is necessary to heat very strongly 
towards the end, in order that the centre of the mass may 
receive a sufficient amount of heat to effect its decomposition. 
Naked glass retorts cannot be used ; and either coated glass 
or porcelain retorts must be employed. In the large way, as 
in the distillation of amalgams, &c., cast-iron retorts are used. 

• As before stated, all substances containing mercury, either 
in its metallic state or as oxide, are distilled without addition, 
but with the others it is necessary to employ some reagent, 
which will separate and retain the sulphur, selenium, &c.; 
which reagent may be a metal, as .iron, copper, or tin ; or 
black flux, or a mixture of quick-lime and charcoal: iron 
filings are most often used. For cinnabar about 50 per 
cent, of iron filings is required, in order to prevent any of 
it being sublimed ; the true quantity required is only about 
24 per cent., but an excess is necessary, in order, as before 
stated, to prevent loss: 50 per cent, of iron filings may be 
employed for the selenides, &c. When black flux is 
used, from about 50 to 70 per cent, is employed. Caustic 


ASSAY IN THE DRY WAY. 


455 


lime may be employed in the proportion of 30 per cent, 
mixed with 30 per cent, its weight of charcoal. After the 
ore to be assayed is carefully mixed with any of the above 
fluxes, it is always advisable to cover it, when in the retort, 
with a thin layer of the flux employed, in order to avoid all 
chance of any loss. 

Berthier, who experimented with an ore containing arsenic, 
realgar, &c., and cinnabar from Huanca-Velica, in Peru, 
found, after manifoldly varied fruitless experiments, the 
following method best adapted to its examination for mer¬ 
cury :— 

The ore was heated in a retort with four to five times its 
weight of litharge. From the litharge, the sulphide of 
arsenic, &c., a fusible slaggy mass was formed while the 
cinnabar was decomposed into sulphurous acid and metallic 
mercury. The mercury volatilised completely at a moderate 
heat, and collected in the fore part of the neck of the retort 
and in the receiver. The single precaution which must be 
observed for the success of the assay, consists in onty gradu¬ 
ally and moderately heating the clay or glass retort, in 
order to prevent its being perforated by the corroding 
effect of the litharge before the operation is ended. 

If the assay sample is extremely poor in mercury, the 
ordinary assay method becomes somewhat inconvenient and 
uncertain, on account of the large quantity which must 
then be subjected to distillation in the assay. For this case 
Berthier found it more appropriate to digest the assay 
sample with aqua regia, wash it thoroughly, evaporate the 
whole mass of fluid to dryness, and then treat the dry mass, 
which contains all the mercury as chloride, further in the 
dry way. He found that if chloride of mercury (corrosive 
sublimate) is heated with litharge, it volatilises without 
undergoing any change. If, besides the litharge, coal-dust 
is also added, or if instead of it metallic lead is used in great 
excess, the chloride is reduced to subchloride, which volati¬ 
lises, but not the smallest drop of mercury is thus produced. 
The best reducing agent for the chloride of mercury con¬ 
tained in the dry mass, is black flux, of which three parts 
by weight are used. Since the mass to be subjected to 



456 


THE ASSAY OF MERCURY. 


distillation has been greatly diminished by the treatment 
with aqua regia, and the subsequent evaporation, and no 
high heat is now required for the decomposition, the dis¬ 
tillation may be performed in a glass retort. When the 
gangue in the poor ore is carbonate of lime, all the lime 
is dissolved out, before the treatment with aqua regia, 
by moderately strong acetic acid. 

By this method the smallest trace of mercury in an ore 
or amalgamation product can be shown and determined by 
its weight. 

Assay for the Amount of Cinnabar in an Ore .—The ore 
to be assayed is distilled, without addition, in a glass retort, 
and the sublimed cinnabar collected and weighed. The 
ores containing mercury combined with sulphur are often 
mixed with bituminous matters and carbonate of lime : then, 
when an assay is to be made for cinnabar, it often happens 
that a portion of it is decomposed, either by the carbon 
present, or by the aid of the bituminous matter and lime, 
and a little metallic mercury is driven off with the cinnabar. 
In this case, having weighed the mixture of cinnabar and 
mercury, the mixture is treated by nitric acid, which dis¬ 
solves only the latter, and pure cinnabar remains, whose 
weight is taken, and the quantity of mercury dissolved as¬ 
certained by the difference ; and from that the quantity of 
cinnabar calculated which that quantity of mercury would 
yield. Every 86 parts of mercury furnish about 100 of 
cinnabar. 

If the gangue of the ore be fixed in the lire, the assay 
may be made by mere calcination, and the loss of weight will 
correspond either to the metallic mercury, oxide, or sul¬ 
phide it may contain, 


VOLUMETRIC ESTIMATION OF MERCURY. 

The process we have found most trustworthy is that of 
M. J. Personne, described in the ‘ Comptes Rendus,’ lvi. 63, 
as follows. The author says :— 

‘Two methods have hitherto been used for the estimation 


VOLUMETRIC ESTIMATION OF MERCURY. 


457 


of mercury, the wet and the dry way—one for solid com¬ 
pounds, the other for mercurial solutions. In the wet way 
it is estimated in the state of protochloride, or, better still, 
as metallic mercury by means of appropriate reducers, or as 
a sulphide. This method, which necessarily occupies a long 
time, is not always so exact as might be desired. The dry 
way, though more easily executed, and giving more exact 
results, still requires a considerable length of time. It applies 
but indirectly to the estimation of a mercurial solution, 
which renders it almost useless in this instance. Being 
under the necessity of estimating a number of mercurial 
solutions by a certain time, I was compelled to find some 
more certain and rapid means of estimation than either of 
those I have enumerated. The following is the result of my 
investigations. 

4 The process at which I have arrived, after many fruitless 
attempts, is founded on a well-known fact—that a combina¬ 
tion of iodide of mercury with iodide of potassium, form¬ 
ing the double iodide of Polydore Boulay, HgI,KI, gives a 
colourless solution. Thus, two solutions in equal quantities, 
one containing one equivalent of bichloride of mercury, the 
other two equivalents of iodide of potassium, being mixed, 
by pouring the mercurial solution into that of the iodide of 
potassium, iodide of mercury will be produced by the 
contact of the two solutions, which dissolves in proportion 
to its formation, until the mercurial solution added is equal 
in volume to that of the alkaline iodide used, according to 
the following equation :— 

HgCl+ 2KI=HgI,KIpKCl. 

The slightest excess of bichloride causes the formation of a 
persistent red precipitate, giving the liquid a very percep¬ 
tible red tint even by artificial light. This coloration, which 
indicates that the saturation is complete, gives to this mode 
of estimation a precision and nicety quite as great as that 
of litmus used to ascertain the saturation of an acid by a 
base. The mercurial solution must always be poured into 
the alkaline iodide, not die alkaline iodide into the mercu¬ 
rial solution ; otherwise, though the last reaction may be the 


458 


THE ASSAY OF MERCURY. 


same, it is impossible to obtain exact results, because the 
iodide of mercury produced, not being brought simul¬ 
taneously with its formation (in a nascent state) into contact 
with the alkaline iodide with which it is to combine, be¬ 
comes sufficiently cohesive to dissolve but slowly in the 
iodide of potassium. Thus, in operating with the same 
liquids, the quantity of alkaline iodide which must be added 
to dissolve the iodide of mercury precipitated varies ac¬ 
cording to the time employed in effecting the estimation, 
and that in considerable proportions. I have no doubt that 
it is through operating in this way that iodide of potassium 
has hitherto been rejected as a medium for the exact es¬ 
timation of mercury. 

4 Two normal liquids are necessary to effect this estima¬ 
tion. 

4 1. Normal Standard Solution of Iodide of Potassium .— 
Obtained by dissolving 33*20 gr. of pure iodide of potas¬ 
sium in water enough to make 1 litre of solution. 10 
cubic centimetres of this solution represent 0*1 of metallic 
mercury. 

4 2. Normal Standard Solution of Bichloride of Mercury .— 
Prepared by dissolving 13*55 gr. of bichloride of mercury 
in water so as to make 1 litre of solution. The solution of 
mercurial salt is facilitated by the addition of 5 equivalents, 
or 30 grammes, of chloride of sodium, which has no influ¬ 
ence on the reaction, like all neutral alkaline salts ; 10 cubic 
centimetres of this solution also represent 0*1 of mercury. 
Of these 10 centimetres, divided into 100 parts, each division 
represents 0*001 of mercury. This mercurial solution serves 
to test the purity of the alkaline iodide solution or to give 
the standard of an unknown solution. 

4 Liquids ten times more diluted may be prepared without 
injuring the nicety of the reaction or the exactness of the 
results ; fractions of a milligramme may thus be estimated. 

4 The estimation is effected in the following manner .*_ 

10 cubic centimetres of a normal solution of iodide beiim 
measured into a small saturating vessel, pour into it, con¬ 
stantly shaking the vessel, the solution of bichloride, 
measured in Gay-Lussac’s burette. If the two liquids are 


VOLUMETRIC ESTIMATION OF MERCURY. 


459 


pure, it will require exactly 100 divisions of the burette 
before the light red tint appears in the saturated liquid to 
indicate the close of the operation. When the mercurial 
solution is weak a proportionally larger quantity must be 
added ; if, on the other hand, it is too strong, less must be 
added. As will be perceived, this is very similar to the 
chlorometric process. 

4 This new method of estimating mercury being applicable 
only to bichloride, it became desirable to extend its applica¬ 
tion to a greater number of mercurial compounds, if not to 
all. This side of the question presented difficulties not 
easily resolved in a satisfactory manner. It was, in fact, 
necessary to transform all the mercurial compounds into a 
perfectly neutral solution of bichloride. I was obliged to 
set aside successively the use of aqua regia, and even of 
hypochlorous acid. The great volatility of bichloride of 
mercury, even in a boiling solution, caused too great a loss. 
M. Pivot’s process—that is to say, the action of chlorine in 
a solution of hydrate of potash or soda—is perfectly success¬ 
ful. Take, for instance, the estimation of mercury in cinna¬ 
bar. Peduce one gramme of cinnabar to a fine powder. 
Weigh it on paper, and introduce it into a matrass. Pour 
into the matrass 20 cubic centimetres of a caustic soda 
solution, with which mix the paper and its contents by 
quickly shaking; then send a current of chlorine, which 
need not be washed, into the liquid. The action of the 
chlorine produces a slight heat, which is gradually brought 
to boiling-point, by which time all the matter will have 
disappeared. To ensure success, the temperature must be 
carefully managed at the commencement. If it is raised 
too quickly, part of the matter remains undissolved. The 
solution being complete and saturated with chlorine, it is 
kept boiling long enough to expel all the excess of chlorine. 
The boiling may be prolonged without incurring any loss 
of bichloride, which is not volatile in presence of alkaline 
chloride. The solution when cooled is poured into a gradu¬ 
ated tube. The matrass as well as the tube for conducting 
the chlorine are washed two or three times witli water, and 
the washing added to the original liquid, so as to form 100 



460 


THE ASSAY OF MERCURY. 


cubic centimetres of solution. I effected the estimation 
with the standard solution of iodide, of which 10 centimetres 
represent 10 of mercury. To saturate these 10 centimetres 
it required 115 divisions of the chloromercurial solution. 
These 115 divisions contain then 0T0 of mercury. Now, 
as all the mercury contained in the analysed cinnabar is 
spread through the 10,000 divisions of solution, we have 
the quantity of mercury found by the experiment by means 
of a simple proportion.’ 

BLOWPIPE REACTIONS OF MERCURY. 

Mercury. —The compounds of mercury are all volatile, 
and cannot, in consequence, be distinguished by their re¬ 
action with any of the fluxes. Substances containing mercury 
are assayed by being mixed with a little tin, iron filings, or 
oxide of lead, and heating the mixture to redness in the 
closed tube or matrass. In this operation the mercury is 
reduced, and collects in the coldest part of the tube as a 
greyish powder, which being brought together by the end 
of a feather, collects as metallic globules. When the quantity 
is very small, the globules may be distinguished by aid of 
the microscope. 


ORES OF MERCURY. 

Cinnabar, Sulphide of Mercury.— Alone, on charcoal, it 
volatilises without residue, giving off an odour of sulphurous 
acid. In the matrass it sublimes, giving a blackish subli¬ 
mate. In the open tube,- it gives, by roasting, mercury and 
sublimed cinnabar. In the matrass, with soda, globules of 
mercury are obtained. 

Chloride of Mercury, Horn Mercury. —On charcoal, vola¬ 
tilises without residue. In the matrass, gives a white subli¬ 
mate. With soda, in the matrass, gives much mercury in 
globules. 

With microcosmic salt, fused on the brass wire, it commu¬ 
nicates a fine azure blue colour to the flame, indicative of 
chlorine. 


461 


CHAPTEE XV. 

ASSAY OF SILVEE. 

All argentiferous substances may be divided into two classes, 
as follows :— 

Class I.—All minerals containing silver, 

Silver glance (AgS) containing 87 per cent, of Ag. 

Brittle silver ore (6AgS,SbS 3 ) containing 70,4 per cent, of Ag. 

Light red silver ore (3AgS,AsS 3 ) containing 65,4 per cent, of Ag. 

Dark red silver ore (3AgS,SbS 3 ) containing 59 per cent, of Ag. 

Light and dark fahlerz (argentiferous grey copper ore), containing 
from 5,7 to 18-31’8 per cent, of Ag. 

Argentiferous sulphide of copper (Cu 2 S,AgS) containing 53 per 
cent, of Ag. 

Polybasite (9(Cu 2 S,AgS) -f (SbS 3 ,AsS 3 )) containing 72-94 per cent, 
of Ag. 

Slags. 

Cupel bottoms. 

Dross. 

Litharge, etc. 

Class II.—Metallic silver and alloys, either native or 
otherwise. 

General Observations on the Assay of Ores and Substances 

of Class No. 1.' 

In order to separate silver from this class of substances, an 
alloy of the precious metal with lead must be formed. The 
different methods by which this object can be obtained are 
the following : firstly, fusion with a reducing flux ; secondly, 
fusion with oxidising reagents ; thirdly, scorification. 

All substances containing lead in the state of oxide, such 
as carbonates, phosphates, &c., are fused directly with a 
reducing flux, as also are slags, old cupels, litharge, &c. All 
plumbiferous sulphides, &c., containing silver, are assayed 
as for lead by the processes already pointed out, taking care 



462 


tup: assay of silver. 


to follow the method which gives the largest proportion of 
lead. 

All argentiferous minerals containing copper may be 
assayed as copper ores ; because an alloy of copper and silver 
can be cupelled by means of lead. 

In making assays of silver with lead or copper, it is 
sometimes necessary to commence the operation by roasting 
the ore; under other circumstances, also, argentiferous 
matters are roasted. 

There is nothing very particular to be observed in this 
roasting; the temperature alone requires attention by 
managing well at the commencement of the operation, in 
order to avoid softening, and especially to avoid a very 
rapid disengagement of arsenical vapours, because a very 
considerable amount of silver may be lost by that means. 

All substances which contain reducible oxides are fused 
with a reducing flux, as also those from which charcoal 
separates metals which alloy with lead, or metals which do 
not hinder the process of cupellation ; but it is necessary to 
add to the reducing flux a certain proportion of litharge, in 
order to produce metallic lead, with which the silver may 
alloy. A mixture of metallic lead and any suitable flux may 
be substituted for that of litharge and a reducing flux ; but 
the latter is preferable, because the lead produced is 
uniformly diffused throughout the whole mass of flux, &c., 
not allowing a particle of silver to escape its action. 

The reducing agent employed in nearly all assays is 
charcoal either in its ordinary state, or as it is found in 
black flux. Starch and other analogous substances may be, 
as before mentioned, substituted for it: crude argol is, how¬ 
ever, the best reducing agent. The portion employed must 
be varied according to circumstances, so that the silver-lead 
produced be not too rich, or that too great a proportion of 
lead be reduced. If the silver-lead be too rich, much of 
the precious metal may be lost in the slag, and if too great 
a quantity of lead be produced, silver is again lost, owing to 
the long exposure to the fire during cupellation ; and indeed 
this is the most fruitful cause of loss, for more is lost in this 
manner than by having too little lead produced. In order to 


FUSION WITH OXIDISING REAGENTS. 463 

know the right proportions, the following data will serve as 
a guide :—1 part of charcoal reduces about 30 parts of lead 
from litharge, and 1 part of black flux reduces about 1 part 
of lead. 

The iluxes employed in this kind of assay are litharge, 
black flux, carbonate of potash or soda, and borax. Litharge 
is an exceedingly convenient flux, because it occupies very 
little room, and fuses without bubbling, producing very 
liquid scoria with nearly every substance. Experiment has 
shown that nearly all argillaceous, stony, and ferruginous 
substances fuse very well with from 8 to 12 or more parts 
of litharge. If from J* to 1 part of black flux, or -J^th to 
^-g-th of charcoal, be added to 1 of ore, from ^ a part to 1 
part of silver-lead will be produced. 

Black flux is employed in the fusion of all substances 
containing a large proportion of alumina, or in which lime 
is the predominant substance : from 2 to 3 parts of this flux 
generally suffice : 1 part of litharge is added to the assay, 
which is wholly reduced, producing nothing but lead. 

The carbonates of potash or soda produce exactly the 
same effects as the alkali of the black flux. A certain 
quantity of charcoal must, in this case, be added to the assay. 

Schlutter fuses the poor refuse of goldsmith’s workshops, 
mixtures of fragments of crucibles, glass, &c., with 2 parts 
of carbonate of potash, when they are very earthy, and with 
1 part only, when they contain much glass, adding, at the 
same time, to the mixture, a little litharge and granulated 
lead. 

Borax has, like litharge, the advantage of being an 
universal flux ; it is useful especially for the fusion of sub¬ 
stances containing much lime; but it is necessary to take 
great care in the assay, in order to avoid the loss which its 
boiling up might occasion. This only applies, however, to 
its use in its ordinary state ; if previously fused, that is, used 
as glass of borax, no particular care need be taken. 

FUSION WITH OXIDISING REAGENTS. 

Litharge .—The oxidising agents employed in the assay of 
argentiferous substances are litharge and nitre. Litharge 


464 THE ASSAY OF SILVER. 

attacks all the sulphides, arsenio-sulphides, &c., and oxidises 
nearly all the elements, excepting silver, when employed in 
sufficient quantity, and a quantity of lead equivalent to the 
oxidisable matters present is reduced, so that there results 
from the assay a slag containing an excess of oxide of lead, 
and an alloy of lead and silver, very little contaminated with 
foreign metals, if no copper be present, and which can be 
submitted directly to cupellution. This method of assay is 
exceedingly convenient and quick. 

The pulverised mineral is well mixed with litharge, and 
the mixture placed in a crucible, which may be very nearly 
filled, as there is scarcely any boiling up when the pot and 
its contents are submitted to the fire. A thin layer of pure 
litharge is placed above the mixture, the whole is then heated 
rapidly, and as soon as the litharge, &c., is completely fused, 
the crucible is taken from the fire. It is inconvenient to heat 
it for any length of time, on account of the corrosive action 
litharge has on the substance of the crucible, which it rapidly 
destroys. 

The proportion of litharge which must be employed 
depends upon the nature and quantity of oxidisable matters 
present in the ore. It ought in general to be very great, 
because it is absolutely necessary that no sulphurous matters 
be present, so that the slag may not contain the least trace 
of silver. But it is known how much litharge is required to 
decompose the metallic sulphides. Pyrites requires about 
50 parts ; mispickel, blende, sulphide of antimony, copper 
pyrites, grey cobalt, and grey copper, require from about 
twenty-five to about forty times their weight. For sulphide 
of bismuth 10 are sufficient, and for galena or sulphide of 
silver but 4 or 5 parts need be employed. The proportion 
of litharge will not be so great for a mineral containing 
much stony gangue as for one entirely metallic. Experiment 
has proved, that the assay of rough schlichs, such as those 
treated in the large way by amalgamation, can be made very 
exactly with from 10 to 12 parts of litharge. 

Alloys of silver with the very oxidisable metals can be 
assayed by means of litharge, such as those of iron, antimony, 
tin, zinc, &c. ; but in order to have a successful result the 


FUSION INTO OXIDISING REAGENTS. 


465 


alloys should be reduced to a very fine state of division, so 
that they must be at least granulated; and it is very often 
necessary to repeat the operation several times on the fresh 
alloy of lead produced. 

The method of assay just pointed out is inconvenient, on 
account of the large quantity of lead it produces ; pyrites 
giving 8i parts, copper pyrites and blende 7 parts, sulphide 
of antimony and grey copper about 6 parts, &c. In order 
to avoid this inconvenience, part of the oxidation can be 
performed by means of nitre. Nitre alone, employed in 
excess, oxidises all metallic and combustible substances found 
with silver, and even, under certain circumstances, a portion 
of the silver itself; but when the proportion is insufficient to 
oxidise the whole, and when the mixture contains at the 
same time litharge, after the nitre has produced its action, 
the litharge acts in its turn on the remainder of the oxidi- 
sable substances, and the resulting lead carries down the 
silver set free. So that, by employing suitable proportions 
of nitre and litharge, all the silver contained in oxidisable 
minerals may be extracted, and any quantity of lead required 
may be thus alloyed with it. 

As to the requisite proportion of nitre, it can be come at 
by practice, aided by the following data. It requires about 
parts of nitre to completely oxidise, iron pyrites, IJ> for 
sulphide of antimony, and § for galena. 

This determination can be ascertained at once as follows : 
fuse 1 part of the mineral with 30 of litharge, and weigh 
the resulting button of lead ; and having fixed upon the 
quantity of lead necessary to carry on the cupellation pro¬ 
perly, deduct it from the whole weight of the button, and 
the difference will be the amount of lead necessary to leave 
the slag in the state of oxide; and as it has been proved 
by experiment that 1 part of lead requires *25 to *30 of 
nitre, that is, from 25 to 30 per cent., it is easy to calculate 
the quantity necessary to be added. 

When the ore contains sulphur, the latter forms with the 
nitre sulphate of potash, which swims on the slag without 
combining with it. 

The assay of silver ores by means of nitre is advantageous 

H H 


466 


THE ASSAY OF SILVER. 


and useful in a variety of cases. If we wish to determine, 
for example, very exactly the percentage of silver in a poor 
galena, a large quantity, say | of a pound, must be fused 
with about an ounce or an ounce and a half of nitre, and a 
quarter of a pound of carbonate of soda, or better still, the 
same quantity of litharge, one of either of which must be 
employed to flux the gangue and temper the deflagration. 
After the fusion, all the contained silver will be found alloyed 
with a very small quantity of lead. 

Sometimes the assay is made with a larger quantity of nitre 
Jian is requisite for the oxidation, and when the mixture is 
perfectly fused a certain quantity of metallic lead is added, 
taking care to cover the whole surface of the mixture, 
either by using granulated lead or a convenient mixture of 
litharge and charcoal, or litharge and galena. The shower 
of metallic lead passing through the fluid mass alloys with 
all the silver it finds in its passage, and so concentrates it. 

This process, however, cannot always be confidently 
employed. If an excess of nitre be employed with sub¬ 
stances susceptible of forming peroxides capable of attack¬ 
ing silver, such as some cupreous substances, the lead 
added reduces the greater part, but not the whole of the 
silver in the ore, so that the assay will not be perfect. 

Special Directions for the Crucible Assay of Ores and 
Substances of the First Class. 

The ores and substances belonging to this class may, for 
the convenience of assay, be further subdivided on the 
following principle. It has already been seen that sulphur, 
and other substances having a great affinity for oxygen, 
reduce metallic lead from litharge in proportion to the 
amount of reducing matter present; and as it is necessary 
in this kind of assay that no more than a certain quantity 
of lead alloy should be submitted to cupellation, some kind 
of control must be- exercised by the assayer, to keep the 
quantity of lead reduced in due and proper bounds. This 
is readily accomplished by what is called a 4 preliminary 
assay, 'by which all ores and substances of this class 


SPECIAL DIRECTIONS FOR TIIE CRUCIBLE ASSAY. 


467 


are divided into three sections:—lstly, ores which, on 
fusion with excess of litharge, give no metallic lead, or less 
than their own weight; 2ndly, those which give their own 
weight, or nearly their own weight, of metallic lead ; ordly, 
those which give more than their own weight of metallic 
lead. The preliminary or classification assay is thus con¬ 
ducted :— 

Carefully mix 20 grains of the finely pulverised ore (all 
silver ores must be passed through a sieve with 80 meshes 
to the linear inch) with 500 grains of litharge ; place the 
mixture in a crucible which it only half fills; set the 
crucible, after careful warming, in a perfectly bright fire, 
and get up the heat as rapidly as possible, so as to finish 
the operation in a short time, to prevent the action of the 
reducing gases of the furnace on the oxide of lead, because, 
if a great length of time were taken in the operation, a 
portion of the lead reduced might be traceable to the fur¬ 
nace gases, and the result of the experiment vitiated. After 
the contents of the crucible are fully fused, and the surface 
perfectly smooth, the crucible may be removed and allowed 
to cool, and when cold broken. One of three circumstances 
may now present itself to the assayer : lstly, no lead, or less 
than 20 grains, has been reduced; 2ndly, 20 or nearly 20 
grains, more or less, may be reduced ; apd 3rdly, more than 
20 grains may have been reduced. 

Now, as it has been already stated, 200 grains of lead 
alloy is a suitable amount to cupel; and as 200 grains is the 
best quantity of ore to submit to assay, it will be evident 
that ores and substances of the second section, or those 
bodies which give their own weight, or nearly their own 
weight, of lead alloy, simply require fusion with a suitable 
quantity of litharge and an appropriate flux. Ores of the 
first section require the addition of a reducing agent, in 
quantity equivalent to the standard amount of lead alloy 
(200 grains) ; and ores of the third section require an equi¬ 
valent quantity of an oxidising agent, or an amount of some 
body which will oxidise the lead in excess of 200 grains of 
alloy. 

The reducing agent employed is argol; the oxidising 

H H 2 


468 


TIIE ASSAY OF SILVER. 


agent, nitrate of potash. It is necessary, before commenc¬ 
ing an assa} 7 of a silver ore, to determine how much lead a 
given weight of the argol the assayer has in use will reduce, 
as also how much lead a given weight of nitrate of potash 
will oxidise. These assays are thus made:— 

Assay of Reducing Power of Argol. —Carefully mix 20 
grains of the argol to be tested with 500 grains of litharge 
and 200 grains of carbonate of soda; place the mixture in 
a suitable crucible, and cover with 200 grains of common 
salt. (It is best to mix two such quantities, and take the 
mean of the results.) Fuse with the precautions pointed 
out in assay of substances of the first class, containing lead. 

Weigh the resulting buttons, and take a note of the mean 
weight, which will represent the amount of lead reducible 
by 20 grains of argol. 

Assay of Oxidising Power of Nitrate of Potash. —Mix 20 
grains of finely powdered nitrate of potash, 50 grains of 
argol, 500 grains of litharge, and 200 grains of carbonate of 
soda ; cover with 200 grains of common salt, and fuse as 
above. Weigh the resulting button. How calculate the 
amount of lead which should have been reduced by 50 
grains of argol, and the difference between that and the 
amount of lead reduced in this experiment will represent 
the amount of lead oxidised by 20 grains of nitrate of 
potash. 

Thirty to 32 grains of ordinary red argol reduce about 200 
grains of lead ; and 23 grains of pure nitrate of potash 
oxidise about 100 grains of lead. The assayer must, how¬ 
ever, adopt the numbers found by himself by experiment, as 
the samples of argol and nitre may be more or less impure. 
He must also examine every fresh supply of litharge for the 
amount of silver it contains, in the following manner :— 

Assay of Litharge for Silver. —Mix 1,000 grains of 
litharge with 30 grains (or any other quantity that may be, 
by experiment, found requisite) or argol, 200 grains of car¬ 
bonate of soda, and cover with salt, as already directed. 
Fuse the mixture in a suitable crucible; allow it to cool; 
break and cupel the button obtained, as hereafter to be de¬ 
scribed : take a note of the amount of silver obtained ; and 
as 1,000 grains of litharge is the standard quantity for a 


ASSAY OF ORES OF THE SECOND SECTION. 


469 


silver assay, the amount of silver, indicated as above, is to 
be deducted from the amount of silver obtained in the assay 
of any silver ore, until that quantity of litharge is consumed. 

Assay of Ores of the First Section .—Make a preliminary 
assay, as already described. Suppose 10 grains of lead 
result; then, as 20 have furnished 10 grains, so 200 grains 
of ore would furnish 100 grains of lead, or 100 grains less 
than the quantity best adapted for cupellation; so that, re¬ 
ferring to the assay of argol, and finding that from 30 to 32 
grains reduce 200 grains of lead, then it is clear that the re¬ 
ducing power of from 15 to 16 grains of argol, in addition 
to the reducing power of 200 grains of ore, is necessary to 
furnish 200 grains of lead alloy. In this case, the ingredients 
required in the actual assay, or ‘ assay proper,’ would stand 
thus :— 

200 grains of ore. 

200 grains of carbonate of soda. 

* 1,000 grains of litharge. 

15 to 16 grains of argol. 

These materials are to be thoroughly well mixed, placed 
in a crucible which they about half fill, and covered first 
with 200 grains of common salt, and then 200 grains of 
borax, and submitted to the fire with the usual precautions; 
when the flux flows smoothly the assay is complete; it may 
be removed and allowed to cool, the crucible broken, and 
the button obtained must be hammered into a cubical form, 
and should approximate to 200 grains, either more or less, 
within 10 grains. Two crucibles must always be prepared. 
It will also be here convenient to mention that the argol and 
nitrate of potash are the only substances whose quantities 
vary in the assay of silver ores, the amount of these varia¬ 
tions being determined by the preliminary or classification 
assay. 

Assay of Ores of the Second Section .—If the preliminary 
assay of the sample submitted to assay furnish from 18 to 22 
grains of lead, then the assay proper may be thus made :— 

200 grains of the ore, 

200 grains of carbonate of soda, 

1,000 grains of litharge, 


470 


THE ASSAY OE SILVER. 


well mixed, and covered with, salt and borax as above. 
Fuse with due care, and reserve buttons of lead alloy for 
cupel lation. 

Assay of Ores of the Third Section .—If the sample on 
preliminary assay furnished 40 grains of lead, then the 200 
grains employed in assayproper would give 400 grains, or 200 
grains of lead in excess: refer now to note-book for quan¬ 
tity of lead oxidised by nitre : suppose the nitre pure as just 
stated, 23 grains will oxidise 100, therefore 46 grains are 
equivalent to 200, and the assay proper will stand thus:— 

200 grains of the ore. 

200 grains of carbonate of soda. 

1,000 grains of litharge. 

46 grains of nitrate of potash. 

The nitrate of potash is to be weighed first, finely pulverised, 
and then well mixed with the remaining substances, and 
covered with salt and borax. The crucible in this assay must 
be larger than in the two preceding cases ; the mixture should 
not more than one-third fill it, as there is a considerable 
action set up between the oxygen of the nitre and the sul¬ 
phur or arsenic, or any other substance that may be the 
reducing agent in the ore ; for in fact the nitre does not 
directly oxidise the lead, which sulphur, &c., might have re¬ 
duced, but oxidises its equivalent quantity of sulphur, or 
whatever other reducing substance there may be in the ore, 
so as only to leave a sufficient amount to reduce 200 grains 
of lead, in lieu of the 400 as indicated by preliminary assay, 
or when the reducing power of the ore was allowed to come 
into full play. The buttons obtained in this case are also 
to be reserved for cupellation. 

Scorification .—Scorification has, like fusion with litharge, 
the effect of producing an alloy of lead capable of cupella¬ 
tion, and a very fusible slag composed of oxide of lead, and 
all the matters foreign to silver, converted into the state of 
oxide. In the crucible assay as just described the oxidation 
of these substances takes place by the action of the litharge, 
which furnishes at the same time by its reduction the lead 
necessary to form the alloy, whilst in scorification all the 


SCORIFICATION. 


471 


substances susceptible of oxidation are oxidised in the roast¬ 
ing by means of the oxygen of the air, and the litharge itself 
is produced by the oxidation of part of the lead mixed with 
the ore to be assayed. 

In this operation vessels termed scorifiers (see p. 131) are 
employed. They are heated in the muffle of the cupelling 
furnace, and as many assays may be made at one time as 
the muffle holds scorifiers. 

Before introducing the scorifiers into the muffle, a given 
weight of the ore reduced to powder is mixed intimately 
with a certain quantity of granulated lead, and placed in 
each. They must then be heated gradually for about a 
quarter of an hour, with the door of the muffle closed, in 
order to fuse the lead; then diminish the heat, and allow 
access of air by opening the door. The current thus esta¬ 
blished in the muffle soon causes the commencement of the 
roasting ; and this roasting goes on without its being neces¬ 
sary to continually agitate the mass, as in the case of pul¬ 
verulent substances. 

During the oxidation, a slag is formed on the fluid metal, 
which is thrown towards the edges, and which, by continu¬ 
ally augmenting, at last entirely covers the bath. This slag, 
which is often solid at the commencement, becomes softer 
and softer, and at last becomes perfectly fluid ; because, in 
proportion to the advance of the operation, the proportion 
of oxide of lead continually increases. When it is judged 
that the scorification has been carried far enough, the melted 
matter is stirred with a rod of iron, in order to mix with the 
mass the hard or pasty parts attached to the bottom or sides 
of the scorifier. The fire is then urged so as to completely 
liquefy the slags. It may be ascertained when they are suf¬ 
ficiently fluid by plunging into them a red hot iron rod, 
which must only be covered with a slight coating, capable 
of running off, and not solidifying into a drop at the end. 

This condition of liquidity is indispensable, in order to 
enable the metallic globules to unite into a single button. 
When this end is not attained, it is because the scorification 
has not been carried sufficiently far, or because a sufficient 
quantity of lead has not been added to form the flux, in which 


472 


THE ASSAY OF SILVER. 


case a fresh quantity must be added, or, what is preferable, 
the assay recommenced with larger proportions. 

When the operation is finished, the scorifier must be re¬ 
moved, and its contents immediately poured into a circular 
or hemispherical ingot mould (see fig. 27, p. 66). The 
metallic particles fall to the bottom, and as the cooling pro¬ 
ceeds they form a button covered by the. slag, which is 
readily detachable by a blow of a hammer : it ought to be 
very homogeneous and vitreous, and its colour varying from 
brown to greenish. 

It is always advisable to examine it, and ascertain if it 
contain metallic globules. The button ought to be as ductile 
as ordinary lead; if not it cannot be cupelled, and must be 
submitted to a fresh operation. It is in general advanta¬ 
geous to push the scorification to its greatest extent, because 
experiment has proved that less silver is lost than when a 
large button is cupelled. Nevertheless, there is a limit, be¬ 
cause if the silver-lead produced be too rich, the least loss in 
the shape of globules would cause a notable one in the silver. 
Besides, as litharge exercises a very corrosive action on 
earthy matters, if the scorification be continued for a great 
length of time it sometimes happens the vessel is pierced, 
and the assay has to be recommenced. The button of lead 
remaining ought to weigh about 200 to 300 grains, when the 
ores treated are of ordinary richness. The length of time a 
scorification takes is from half an hour to an hour. The 
scorifier can be rendered less permeable to the litharge 
by being rubbed inside with chalk, or better still red 
ochre. 

There may be distinguished three distinct periods in the 
operation, viz. the roasting, the fusion, and the scorification. 
At first a strong fire is employed ; but the doors of the 
furnace are opened as soon as the mixture is fused. The 
mineral, being specifically lighter than the lead, is then 
seen floating on its surface, or forming masses in it; the 
roasting then commences, and from the appearance of the 
vapours, the nature of the combustible matter it contains 
may be judged. Sulphur produces clear grey vapours : zinc, 
blackish vapours, and a brilliant white flame: arsenic, 


SCORIFICATION. 


473 


whitish-grey vapours: antimony, fine red vapours, &c. 
When no more fumes are seen, the mineral has disappeared, 
and the fused lead perfectly uncovered, the roasting has ter¬ 
minated : this generally requires from eighteen to twenty 
minutes. At this time the fire is urged, so as to cause all 
the substances in the scorifier to fuse. It can be asertained 
that the fusion is complete, by the following signs : at the 
instant the muffle is opened, the button becomes whitish-red 
with a greyish-black band, and there arise from the melted 
mass clear white fumes of lead, and the slag appears like a 
ring encircling the metal. The third period then com¬ 
mences : the furnace is cooled, as in the roasting, and the 
lead is allowed to scorify until it is entirely covered with 
fused oxide : this last period generally lasts about fifteen 
minutes. The fire is then increased for about five minutes, 
and the contents of the scorifier poured into the mould. 

The process of scorification is applicable to all argentifer¬ 
ous matters, and is at the same time the most exact method 
of assay, as also the most convenient, when a large number 
of assays are required at the same time, because they are 
entirely executed in the muffle, which, with most assayers, is 
generally hot: it, however, requires a greater number of 
vessels—as cupels, &c. 

When the silver ores are stony, the oxide of lead formed 
during the roasting combines with the gangue, forming a 
fusible compound, whilst the remaining lead alloys with the 
silver. When the ores are metallic, the oxidisable bodies 
absorb oxygen from the atmosphere; and the oxides so 
formed combine with the litharge produced at the same 
time, forming a compound which becomes very fusible in 
proportion as the oxide of lead increases ; and if the scorifi¬ 
cation has not been pushed sufficiently far, the button will 
contain, besides silver and lead, a little copper, which will 
not, however, interfere with the cupellation. There is this 
one peculiarity about scorification, that however small the 
proportion of lead may be that is used, at the end of the 
operation the slag does not contain any oxysulphide. For 
instance, even when oxysulphides are produced in the course 
of scorification, they are completely decomposed in the 


474 


TIIE ASSAY OF SILVER. 


roasting, and in consequence it is very rarely that the slag 
retains any proportion of silver; and as to the propor¬ 
tion of lead employed, only just enough to render the slag 
liquid, and to produce sufficient lead for cupellation, is ne¬ 
cessary. 

It is different, however, when the sulphides and arsenio- 
sulphides are assayed by means of litharge; for from 30 to 
50 parts of that substance must be employed to prevent the 
scoria retaining any silver, or, as already pointed out, 
a certain proportion of nitre must be added. 

All scorifications may be conducted by the simple addition 
of lead; but it has been proved that the operation proceeds 
more quickly, and with less danger to the scorilier, when 
borax is employed. This salt dissolves the oxides in pro¬ 
portion as they are produced, as also the gangues, and forms 
a very liquid slag from the commencement of the operation, 
which does not happen when lead alone is used, because 
litharge, which can alone cause the fusion, is only present in 
the slag in sufficient proportion at a very advanced stage 
of the operation. 

When the slag is liquid at the beginning of the operation 
(as occurs in the use of borax), it is continually thrown on 
the sides of the scorilier, and forms a ring on the surface of 
the bath, leaving in the centre the metallic substance, having 

C 7 O 

a considerable extent of surface, which is continually 
diminishing. 

The current of air, being thus directly in contact with the 
fused metals, rapidly causes their oxidation, which does not 
take place when the semifluid substances float here and 
there on the metallic bath. The proportion of lead and 
borax necessary for a scorification varies exceedingly, accord¬ 
ing to the nature of the substance under assay, and ought to 
be greater in proportion as the substances, or resulting 
oxides, are difficult of fusion. In ordinary cases 12 parts of 
lead, and 1 of glass of borax, are employed ; but sometimes 
32 of lead, and 3 of borax, are required. A large propor¬ 
tion of borax is useful, especially when the substances con¬ 
tain much lime, oxide of zinc, or oxide of tin. 

Instead of borax, glass of lead may be employed. It acts 


SCORIFICATION. 


475 


as a flux on silica ; but its action is much less effective than- 
that of borax. 

There are some substances which scorify with a small pro¬ 
portion of lead. Thus, for galena and sulphide of copper, 2 
parts of lead suffice ; but 8 parts are required for ores which 
contain much gangue. 

Antimonide of silver can be scorified with 8 parts of lead, 
but according to experiments made in the Hartz, it appears 
that the slag retains about T ^th of silver; with 16 parts 
of lead 2 iroth °f fine metal is still lost; but with 3 of 
borax and 16 of lead not the slightest trace remains in the 
slag. 

It is very difficult to separate tin and silver by the dry way. 
The best method is to roast the alloy in a scorifier, adding to 
it 16 parts of lead and 3 of borax at least, and operating as 
before described. 

Speiss almost always contains silver, and is one of the 
most difficult substances to assay. If nickel be present, the 
button cannot be cupelled. Generally, speiss may be scori¬ 
fied with 16 parts of lead ; and the same operation is gone 
through twice or thrice, adding each time a fresh quantity 
of lead. The operation would probably succeed by roasting 
the speiss in the scorifier before adding the lead. 

Special Instructions for the Scorification Assay of Ores of 
the First Class .—This mode of assay has an advantage over 
the crucible assay just described, inasmuch as if properly 
conducted no preliminary assay is required : but this is 
greatly counterbalanced by the fact that not more than 50 
grains of ore can be operated on in one scorifier, and that 
good or trustworthy results cannot be obtained by this 
method unless four scorifiers are employed for each assay, 
so that in all 200 grains of ore may be employed. There 
are thus employed four scorifiers to three crucibles, and four 
cupels to two cupels; as in one case four burtons are to be 
submitted to cupellation, and in the other only two. When 
very rich copper ores, however, have to be assayed for 
silver, the plan by scorification is very useful, as in the 
crucible operation much copper is reduced with the lead, so 
as to require a very large quantity of leaf! for its convey- 




476 


THE ASSAY OF SILVER. 


•ance as oxide into the cupel. This class of assay will, how¬ 
ever, be particularly noticed under the head Assay of the 
Alloys of Silver. 

Assay in Scorifier. —Weigh out 300 grains of granulated 
lead, place them in a scorifier, then add 50 grains of pulver¬ 
ised fused borax, and 50 grains of the ore to be assayed, 
well mix them in the scorifier by aid of a spatula, and cover 
the mixture with other 300 grains of granulated lead : pre¬ 
pare in this way four scorifiers, place them in the muffle 
with the tongs (5, fig. 26, page 65,) and carefully watch them 
with all the precautions before pointed out: when the sur¬ 
face of the metal is quite covered with fused oxide, pour the 
contents of each scorifier into one of the hollows of the 
mould depicted at fig. 27, page 66. When the mass of slag 
and metal is cold, separate the latter from the former by 
means of the hammer and anvil, hammer the metal into the 
form of a cube, and reserve it for cupellation. 

Assay of Substances of the First Class admixed with 
Native or Metallic Silver .-—The same kind of calculation is 
necessary in the assay of ores as above, as in the case of 
copper ores containing metallic copper. The sample must 
be carefully weighed. Suppose it to weigh 2,500 grains. 
It must be pulverised, and as much as possible passed through 
the sieve with eighty meshes to the linear inch. It will be 
thus divided into two parts : the one passing through the 
sieve is mineralised silver—that is, silver ore of various kinds 
mixed with earthy matter, and a very small quantity of 
metallic silver which has been sufficiently divided to pass 
through a sieve of such a degree of fineness ; the other, 
impure metallic silver, which has been unable to pass through 
the sieve. The weights of both portions are carefully taken, 
and thus noted— 

Rough metallic silver . . . . 5-07 grs. 

Ore through sieve. 2494-93 „ * 

Total weight of sample .... 2500 00 „ 

Assay the ore which passed through the sieve as already 
directed, and the rough silver as directed under the head 
Assay of Silver Alloys. Note the quantity of silver obtained 
in each experiment. Thus: suppose 200 grains of ore 



ASSAY OF SUBSTANCES OF THE FIRST CLASS. 


477 


yielded 2 grains of fine silver, and the 5-07 grains of 
rough silver 4 grains of fine silver by cupellation, the 
number of ounces of fine silver in the ton is thus calcu¬ 
lated. 

On referring to Table III. in Appendix, it will be found, 
that if 200 grains of ore yield 2 grains of fine silver, 
1 ton will yield 326 oz. 13 dwts. 8 grs. of fine silver; 
so that the average produce of the ore is the above 
amount. 

Then, if 507 grains of rough silver yield 4 grains of fine 
silver, 200 grains would yield, by calculation, 159763 grains 
of fine silver. 


Thus— 


200x4 
5-0 7 


159-763 


Now, by referring to Table III. in the Appendix, it will 
be found that 200 grains of ore give 159 grains of fine 
silver = 25, 970 ounces per ton: and that 200 grains of ore 
give 763 grains of fine silver = 124 ozs. 12 dwts. 11 grains: 
therefore, the 5*07 grains of rough silver contain after the 
rate of 26,094 ozs. 12 dwts. 11 grs. per ton, thus— 

25,970 ozs.+ 124 ozs. 12 dwts. 11 grs.=26,094 ozs. 12 dwts. 11 grs. 


Thus we have— 

ozs. dwts. grs. 

Average produce of ore .... 326 13 8 
Average produce of rough silver . . 26,094 12 11 

per ton of 20 cwts. 

Then, as in the case of the copper, multiply the weight 
and produce of each portion together, add the resulting total 
products, and divide the sum by the weight of the sample. 
For this purpose it is better to reduce the pennyweights and 
grains to their decimal values. Thus 13 dwts. 8 grs. is 
nearly equal to *67 of an ounce, and 12 dwts. 11 grs. to *62 
of an ounce ; therefore the quantities above will stand thus 
—326*67 ozs., and 260,94*62 ozs. 


Then 326-67 x 2494-93=815018-7831 
and 26094-62 x 5-07=132296-7234 
and 815018-7S31 + 132299-7234 _ o ~ q g 





478 


THE ASSAY OF SILVER. 


or 378 ozs. 18 dwts. (nearly) per ton of the original sample, 
before pulverising and sifting. 

In every case of assay yet described, it may be mentioned 
that if the sample contained gold, the whole of that metal 
will be found with the silver, as obtained by cupellation, and 
may be separated as stated under the head Gold Assay. 

Cupellation .—Cupellation is one of the most ingenious 
operations that can be imagined ; it has been known from 
time immemorial, has many characters in common with 
scorification, and is effected in nearly the same manner. 
Like that, it has for its end tlie separation of silver and gold 
from different foreign substances, by means of lead ; but it 
differs in this, that the scoriae produced are absorbed by the 
substance of the vessel named a cupel, in which the opera¬ 
tion is made, instead of remaining on the melted metal, the 
latter remaining uncovered and in contact with the air, so 
that the extraneous metals are not only oxidised, but also 
all the lead ; and there remains nothing but the pure metals, 
silver and gold, or an alloy of them in the cupel. 

Cupellation requires, as an indispensable condition, that 
the slag should have the property of penetrating and soak¬ 
ing into the body of the substance forming the cupel; it is, 
therefore, only applicable to a certain number of substances, 
and not to all, like scorification. The oxides of lead and 
bismuth, in a state of purity, are the only oxides which pos¬ 
sess the property of soaking into the cupel; but by the aid 
of one or the other, various oxides which by themselves 
form infusible scorke on the cupel, acquire the property of 
passing through it: therefore, on making a cupellation, it is 
necessary to fuse the substance with a sufficient proportion 
of lead or bismuth, so that the oxides they produce may 
combine with the oxides of all the foreign metals pro¬ 
duced in the operation, and carry them into the body of the 
cupel. 

This proportion varies with the nature of the substances 
cupelled, and other circumstances. The quantity required 
in ordinary cases will be mentioned hereafter. 

The cupels or porous vessels in which the operation is 
made, ought to have a sufficiently loose texture to allow the 
fused oxides to penetrate them easily, and at the same time 


ASSAY OF SUBSTANCES OF THE FIRST CLASS. 


479 


to possess sufficient solidity to enable them to bear hand¬ 
ling without fracture ; and, moreover, they ought to be of 
such a nature as not to enter into fusion with either oxide 
of lead or bismuth. For a description of their mode of 
manufacture, see page 128. 

The following is the method in which an ordinary cupel- 
lation is conducted :—The furnace being heated, the bottom 
of the muffle is covered with cupels, placing the largest 
towards the end ; and if they are required to be heated as 
quickly as possible, they may be placed upside down, and 
turned, at the instant of use, by means of the tongs. When 
the interior of the muffle is reddish-white, the matters to be 
cupelled may be introduced. When the cupels have been 
placed in their proper position, great care must be taken 
from the commencement to blow out of them all cinders, 
ashes, and other extraneous substances which may have 
fallen into them. 

The substance to be cupelled is sometimes an alloy, which 
can pass without addition, and sometimes a compound, to 
which lead must be added. In the first case, the alloy is 
laid hold of by a small pair of forceps, and deposited gently 
in the cupel. In the second case, the substance to be 
cupelled is enveloped in a sheet of lead of suitable weight, 
and placed, as before, in the cupel; or the necessary quan¬ 
tity of lead may be first placed in the cupel, and when the 
lead is fused, the substance to be cupelled added, taking 
care not to agitate the melted mass, and cause loss by splash¬ 
ing. If the substance to be cupelled is in very small pieces, 
as grains or powder, it must be enveloped in a small piece 
of blotting-paper, or, still better, in a piece of very thin sheet 
lead, giving it a slightly spherical form, and dropping it 
gently into the mass of molten metal in the cupel. Some¬ 
times the substance is gradually added, by means of a small 
iron spoon; but it is preferable to use paper, or thin lead, 
as just recommended. 

When the cupels are filled, the furnace is closed, either 
by the door or by pieces of lighted fuel, so that the fused 
metals may become of the same temperature as the muffle. 
When this point has been gained, air is allowed to pass into 
the furnace ; the metallic bath is then in the state termed 



480 


T1IE ASSAY OF SILVER. 


uncovered ; that is, it presents a convex surface, very smooth 
and without slag. When the air comes in contact with it, 
it becomes very lustrous, and is covered with luminous and 
iridescent patches, which move on the surface, and are 
thrown towards the sides. These spots are occasioned by 
the fused oxide of lead which is continually forming, and 
which, covering the bath with a very thin coating of variable 
thickness, presents the phenomenon of coloured rings. 

The fused litharge, possessing the power of moistening (so 
to speak) the cupel, is rapidly absorbed by it when suffi¬ 
ciently porous, so that the metallic alloy is covered and un¬ 
covered every instant, which establishes on its surface a 
continual motion from the centre to the circumference. At 
the same time a vapour rises from the cupels which fills the 
muffle, and is produced by the vapour of lead burning in 
the atmosphere. An annular spot is soon observed on the 
cupel around the metal, and this spot increases incessantly 
until it has reached the edges. 

In proportion as the operation proceeds, the metallic bath 
of silver-lead diminishes, becoming more and more rounded ; 
the shining points with which it is covered become larger 
and move more rapidly ; lastly, as the whole of the lead 
separates, the button seems agitated by a rapid movement, 
by which it is made to turn on its axis ; it becomes very 
lustrous, and presents over its whole surface all the tints of 
the rainbow: suddenly the agitation ceases, the button be¬ 
comes dull and immovable, and after a few instants it takes 
the look of pure silver. This last part in the operation 
of cupellation is termed the brightening , fulguration , or 
coruscation. 

If the button be taken from the muffle directly after the 
brightening, it may throw off portions of its substance; this 
must be avoided, especially when the button is large. The 
button, when covered by mammillated and crystalline 
asperities, is said to have ‘ vegetated.’ The cause of this 
effect seems to be, that when the fused buttons are suddenly 
exposed to the cold air, the silver solidifies on the surface, 
whilst that in the interior remains liquid. The solid crust, 
contracted by cooling, strongly compresses the liquid interior, 


CUPELLATION. 


481 


which opens passages for itself, through which it passes out, 
and around which it solidifies when in contact with the cool 
air. But it sometimes happens that, when the contraction 
is very strong, a small portion of the silver is thrown off in 
the shape of grains, which are lost. 

After brightening, the cupels must be left for a few 
minutes in the furnace, and drawn gradually to the mouth, 
before they are taken out, so that the cooling may be slow 
and gradual. These precautions are nearly superfluous 
when the buttons are not larger than the head of an ordinary 
pin. 

As silver is sensibly volatile, it is essential, in order that 
the smallest possible quantity be lost, to make the cupella- 
tion at as low a temperature as may be. On the other 
hand, the heat ought to be sufficiently great, so that the 
litharge may be well fused and absorbed by the cupel; and, 
moreover, if the temperature be too low, the operation lasts 
a very long time, and the loss by volatilisation will be more 
considerable than if the assay had been made rapidly at a 
much higher temperature. 

Experience has proved that the heat is too great when 
the cupels are whitish, and the metallic matter they contain 
can scarcely be seen, and when the fume is scarcely visible 
and rises rapidly to the arch of the muffle. On the contrary, 
the heat is not strong enough when the smoke is thick and 
heavy, falling in the muffle, and when the litharge can be 
seen not liquid enough to be absorbed, forming lumps and 
scales about the assay. When the degree of heat is suitable 
the cupel is red, and the fused metal very luminous and 
clear. 

. ; In general, it is good to give a strong heat at the com¬ 
mencement, so as to well uncover the bath, then to cool 
down, and increase the heat at the end of the operation for 
a few minutes, in order to aid the brightening. There can 
be no inconvenience in urging the temperature at first, be¬ 
cause the silver-lead is then poor, and much precious metal 
cannot be lost by volatilisation. The increase of fire given 
towards the end is for the purpose of separating the last 
traces of lead, from which it is very difficult to free the 


482 


THE ASSAY OF SILVER. 


silver; but this strong fire must not be continued long, 
otherwise there might be a notable loss by volatilisation. 
When the assay of very poor argentiferous matters is made, 
the heat can be kept up nearly all through the cupellation. 
It generally succeeds better when the temperature is too high 
than too low. 

The force of the current of air which passes through the 
muffle is another very important thing in the success of the 
operation. Too strong a current cools the cupel, oxidises 
too rapidly, and the assay would be spoilt. With a too 
feeble current the operation proceeds slowly, the assay 
remains a long time in the fire, and much silver is lost by 
volatilisation. 

When the litharge is produced more rapidly than it can 
be absorbed by the cupel, or when it is not liquid enough, 
which may happen from the furnace being too cold, or when 
other oxides, produced at the same time, diminish its fusi¬ 
bility, it accumulates gradually on the fluid metal, forming, 
at first, a ring which envelopes its circumference, and which 
gradually extending, covers the whole surface: at this period 
the assay becomes dull, and all movement ceases. When 
the operation is carefully attended to, it is nearly always 
possible to avoid this accident. If, at the first moment, any 
signs are manifested of this evil, the temperature of the 
muffle must be raised, either by shutting the door, or placing 
in it burning fuel: the assay will, in a little time, resume its 
ordinary course. But when the cause of the mishap is sup¬ 
posed to be the abundance of foreign oxides in the assay, a 
fresh proportion of lead must be added. 

It can be ascertained whether an assay has passed well 
by the aspect of the button. It ought to be well rounded, 
white, and clear, to be crystalline below, and readily 
detached from the cupel. When it retains lead, it is 
brilliant below and livid above, and does not adhere at all 
to the cupel. 

In order to detach the button, seize it with a strong 
pair of pliers (see fig. 80), and examine with a micro¬ 
scope (see fig. 81), brushing it to detach small particles 
of litharge which may adhere to it, and place it in 


CU PELL ATI ON. 


4S3 

the pan of a balance (fig. 13, page 24) which will indi¬ 
cate the xoVoth °f a grain. The weight of the silver 
furnished by the lead or litharge employed in the operation 
ought to be subtracted from the amount of silver obtained; 
so that it is necessary to ascertain the richness of these 
matters beforehand, as they nre never completely free from 

Fio. 80. Fig. SI. 



silver. The poorest of them contain from iol -J Xo -th to 

1 th 

TTTTRFTf 111 - 

Sometimes an equal quantity of lead is placed in another 
cupel, and the silver thus obtained placed in the balance pan 
containing the weights. 

F5 O 

Cupellation does not give the exact proportion of silver 
contained in an alloy. There is always a loss, and this loss is 
always greater than that which takes place in the large way, as 
in the latter process a greater quantity is always obtained than 
that determined by the assay. The loss of silver is traceable 
to three causes ; 1st, volatilisation ; 2ndly, to oxidation ; 3rdly, 





484 


THE ASSAY OF SILVER. 


and lastly, to the absolution of minute globules of silver into 
the body of the cupel. It is certain volatilisation takes places, 
because a notable quantity of silver is always found deposited 
on the sides of the furnace and chimney in the shape of dust; 
and silver, which is volatile by itself, becomes much more so 
when alloyed with lead, and is carried away by the vapours 
of the latter, and found in the pulverulent deposits, termed 
lead smoke or fume, which proceeds from the combustion of 
the latter metal in the air. Nevertheless, this cause of loss 
is not very important, for it is rare that the fume contains 
more than yoirwoth of silver, and accurate experiments have 
proved that in cupellation in the small way not more than 
two to three per cent, of lead is volatilised. It is certain 
that a portion of the silver found in cupels which have been 
used for assays exists in the state of oxide, for no part of 
their mass is free—it is found even in the bottom : besides 
it is known that the carbonate of lead precipitated from 
acetate of lead made from litharge contains silver, and a 
notable quantity of that metal is found even in the sulphate 
of lead prepared by means of alum from the acetate (excep¬ 
ting the sulphate is repeatedly washed with water). 

It has been remarked that the centres of cupels which 
have been used for assays are richer in silver than the parts 
nearer the circumference, and that under the button there 
is a spot of bright yellow, which appears to be oxide of 
silver. But the most important cause of loss in an assay is 
the property which the alloys of silver and lead possess of 
introducing themselves into the pores of the cupel. The 
quantity thus lost is in proportion to the coarseness of the 
cupel. For the same quantity of silver, the loss which takes 
place in an assay varies according to the nature of the 
alloy, and the circumstances under which the assay is made ; 
so that it is not possible to form accurate tables of correction. 
This loss is much augmented with the quantity of lead 
employed, but without its being proportionate; so that 
\vhen scorification is had recourse to it is advantageous to 
continue the operation for some length of time, in order 
that the metallic button may be reduced to the smallest 
suitable volume. 



CUPELLATION. 


485 


In the assay of rich alloys, the proportion to the total 
amount of silver is very small, but notable ; and it has been 
calculated for the alloys of copper employed in the arts at 
-swffth ; but in the assay of poor ores, such as galena 
and other minerals treated in the large way, the loss is very 
great, for it is usually as high as 3 -^th. 

By extracting the lead from cupels used in this class of 
assay, the metal furnished contains from about -g~o oWtdh to 
T 5 Wo~o °f silver. The following experiment will give an 
idea of the influence of the proportion of lead on the loss 
of silver : 100 grains of commercial litharge were fused with 
10 grains of black flux, and gave 27 grains of lead, and a 
slag; this was pulverised and reduced in the same crucible 
with 15 grains of black flux, and a second button was 
produced weighing 45 grains. These two buttons being 
cupelled separately, gave, the first *0035 and the second 
•001 only of silver. Three new quantities of 100 grains 
of the same litharge were fused; the first with ^ a part of 
starch, the second with 2 .^, and the third with 10 of the 
same reducing agent. The resulting buttons of lead weighed 
respectively 5'28 and 79 grains. These buttons were 
cupelled, and furnished *0035, *0035, and *003 respectively. 
From these experiments it will be seen that when the litharge 
is not reduced completely, there remains a notable proportion 
of silver in the scoriae ; but, nevertheless, in order to extract 
the largest possible quantity, the whole must not be reduced. 
Indeed, but a twentieth part need only be reduced, because 
more precious metal is lost in the cupellation of a large 
quantity of lead than remains in the portion not reduced. 
The loss of silver in large cupellations is less than that which 
takes place in an assay, because in the large way the litharge, 
or the greater part of it, is run off; whilst in an assay the cupel 
totally absorbs it, so that the latter presents, relatively to the 
same mass of lead, a very much smaller surface in the large 
than in the small way : now it can be readily seen that the 
quantity of silver lost by absorption into the pores of the 
cupel must be proportioned to its surface, all things being- 
equal. ' ' 1 

It has been ascertained by experiment that a cupel 




486 


THE ASSAY OF SILVER. 


absorbs about its own weight of litharge ; so that from this 
fact a cupel of the proper size may be chosen, when the 
weight of lead to be cupelled is ascertained. It is always 
better to have the cupel about ^ or \ as heavy again as the 
lead to be cupelled. 

The various metals found in an alloy, which can be sub¬ 
mitted to cupellation, scorify in proportion to their oxidisa- 
bility. Those most oxidisable scorify with the greatest 
rapidity, and vice versa; so that those which have the 
greatest affinity for oxygen accumulate in the first portions 
of litharge formed, which, by that means becoming less 
fusible, sometimes lose the property of penetrating the 
cupel ; hence the reason why cupellations always present 
more difficulties at the commencement of the operation than 
towards the end when the litharge formed is nearly pure 
oxide of lead, and can contain only oxide of copper. 

The appearance of the cupel used in an assay will give 
indications of the metals the alloy contained. Pure lead 
colours the cupel straw-yellow, verging on lemon-yellow. 
Bismuth, straw-yellow passing into orange-yellow. Copper 
gives a grey, dirty red, or brown, according to its propor¬ 
tion. Iron gives black scoriae, which form at the com¬ 
mencement of the operation, and are generally found at the 
circumference of the cupel. Tin gives a grey slag. Zinc 
leaves a yellowish ring on the cupel, producing a very lumi¬ 
nous flame, and occasioning losses by carrying silver in its 
vapour, and by projecting it from the cupel in its ebullition. 
Antimony and sulphate of lead in excess give litharge- 
yellow scoriae, which crack the cupel; but, when not pro¬ 
duced in too great a proportion, are gradually absorbed by 
the litharge. If the lead alloy submitted to cupellation is 
found to produce this effect, a fresh portion must be mixed 
with its own weight of lead and scorified : the button so 
obtained can now be cupelled. 

Amalgamation .—There are a certain number of argenti¬ 
ferous matters which can be assayed by amalgamation, as 
they are treated in the large way by that method. Amongst 
these are native silver chlorides, sulphides, and arsenio- 
sulphides, which contain neither lead nor copper. 


ASSAY OF THE ALLOYS OF SILVER AND COPPER. 


487 


But this process is seldom had recourse to, because it is 
long, troublesome, and less exact than those just described. 

Substances of the Second Class. 

Native silver. 

Alloys of copper and silver. 

Alloys of other metals and silver (artificial). 

Antimonide of silver. 

Arsenide of silver. 

Telluride of silver (AgTe). 

Auriferous telluride of silver (see gold). 

Hydrargyride of silver (amalgam), (Hg 2 Ag). 

Auride of silver (see gold). 

The following method of separating silver from galena is 
given in the 4 Chemical News,’ vol. ii. p. 239. 

4 Galena consists, as is well known, of the sulphide of 
lead, mixed with a variable proportion of the sulphide of 
silver, and both these substances fuse together, or melt at a 
bright red heat. Now, it so happens that, when sulphide 
of silver is fused with chloride of lead, what is called a 
double decomposition takes place ; that is to say, chloride of 
silver and sulphide of lead are formed. Consequently, if 
we fuse together a quantity of argentiferous galena and 
chloride of lead, we shall remove the whole of the silver 
from the galena, and replace it by sulphide of lead. This, 
then, is the process: mix together the galena and chloride 
of lead in the proportion of 100 lbs. of galena, 1 lb. of 
chloride of lead, and 10 lbs. of chloride of sodium or com¬ 
mon salt; or, if the galena be very argentiferous, add a 
larger amount of chloride of lead. The whole is then fused 
together, when the chloride of silver and common salt rise 
to the surface, and may be skimmed off, and the desilverised 
galena falls and may be run out from the bottom. The 
mixture of chloride of silver and salt may then be decom¬ 
posed by lime and charcoal, or in any other manner, so as to 
reduce the silver and a portion of the surplus chloride of 
lead, by which a metallic mass will result, suitable for the 
operation of the cupel.’ 

General Remarks on the Assay of the Alloys of Silver and 
Copper _The assay of these alloys is nearly always accom¬ 

plished (at least in England) by cupellation. This assay is 


488 


THE ASSAY OF SILVEK. 


most important, as it is by the results obtained in the manner 
hereafter described that the price or value of all kinds of 
silver bullion is determined. 

This class of cupellation is effected without difficulty, 
because the oxide of copper forms so slowly, that the litharge 
is always enabled to pass it into the body of the cupel. 
After having weighed the lead and placed it in the cupel, as 
soon as it is perfectly fused place in it the alloy to be 
assayed, wrapped either in blotting-paper or thin leaf-lead. 
It is essential, in this class of assay, to employ a sufficient 
quantity of lead to carry away all the copper. We may 
always be sure of succeeding, whatever the alloy may be, by 
employing the maximum proportion of lead, that is to say, 
the quantity necessary to pass pure copper; but as the loss 
which the silver undergoes increases with the length of the 
operation and with the mass of the oxidised matters, it is 
indispensable to reduce this loss as much as possible by 
reducing the proportion of lead to that which is strictly 
necessary. Long experience has proved that silver opposes 
the oxidation of copper by its affinity, so that it is necessary 
to add a larger amount of lead in proportion to the quantity 
of silver present. 

M. D’Arcet has obtained the following results by the most 
accurate experiments:— 


Standard of 

Quantity of 

Quantity of lead 

1 

Relation of lead 

silver 

copper alloyed 

- 

necessary 

to copper 

1000 

0 

To ths 

3 


960 

50 

60 to 1 

900 

100 

7 

70 — 1 

SCO 

200 

10 

50 — 1 

700 

300 

12 

40 — 1 

600 

400 

14 

35 — 1 

500 

500 

16 to 17 

32 — 1 

400 

600 

16 — 17 

27 — 1 

300 

700 

16 — 17 

23 — 1 

200 

800 

16 — 17 

20—1 

100 

900 

16 — 17 

18 — 1 

pure copper 

1000 

16 — 17 

16 — 1 


It is remarkable that below the standard of 500, the same 
proportion of lead must be employed, whatever that of 
copper. This fact is repeatedly verified by experiment. 
Whenever fine silver is fused in a cupel, it is always neces* 
sary to add lead, in order to cause the button to unite and . 


















ASSAY OF THE ALLOYS OF SILVER AND COPPER. 


489 


form well. Jt less than T ^ths of lead be employed, the 
button will be badly formed; the litharge cannot separate 
but by the action of a very strong heat, and a considerable 
loss of silver ensues. If, on the contrary, -^ths of lead is 
exceeded, the cupellation goes on well, but the loss is greater 
on account of the duration of the process. These propor¬ 
tions also ought to vary with the temperature. M. Chaudet 
has found, that to cupel an alloy containing y^fo'ths of 
silver, 5 parts of lead are required in the middle of the 
muffle, 10 in the front, and only 3 at the back. 

The proportion of copper carried off by litharge varies 
not only with the temperature, but even for the same tem¬ 
perature in relation to the amount of copper and lead the 
alloy contains. By cupelling 100 parts of copper with 
different proportions of lead in the same furnace, M. Karsten 
obtained the following results :— 


Lead added 

Copper remaining after 
cupellation 

Quantity of lead consumed 
in carrying off 1 of copper 

100 

78-75 

3- 

200 

7012 

7-1 

300 

60-12 

7-7 

400 

49-40 

7-9 

500 

38-75 

8-1 

600 

26-25 

815 

700 

19-75 

8-00 

800 

8-75 

8-70 

900 

5-62 

9-50 

1000 

1-25 

1010 

1050 

o-oo 

10-50 


From which we see that the lead carried away from T Bth to 
jLtli of its weight of copper. Much less lead can be em¬ 
ployed in a cupellation by making the alloy maintain its 
richness of copper throughout the operation. This can be 
accomplished by adding to the alloy in the cupel small 
doses of lead, in proportion as that first added disappears 
by oxidation. If, for example, an alloy composed of 4 parts 
of copper and one of silver be fused with 10 of lead, by 
adding successive small doses of the latter, as already pointed 
out, but 7 parts will be consumed, although in the regular 
way from 16 to 17 would be employed. 

The proportion of oxide of copper contained in the litharge 
increases each instant, and goes on incessantly increasing 









4D0 


THE A SSAY OF SILVER. 


when an alloy of copper and lead is cupelled which contains 
an excess of copper. According to M. Karsten, this propor¬ 
tion is always about 13 per cent, at the commencement, and 
36, or more than a third, at the end of the operation. 

In the assay of the coined alloys of copper and silver, the 
loss of silver may even amount to five thousandths ; but the 
loss is variable, and is proportionally greater as the standard 
of the alloy is lower. 

The following Table contains the results of many experi¬ 
ments made on this subject:— 


Exact standard 

Standard found by cupellation 

Loss, or the quantity of fine 
metal to be added to the stan¬ 
dard as obtained by cupellation 

1000 

998-97 

103 

975 

973-24 

1-76 

950 

947-50 

2-50 

925 

921-75 

3-25 

900 

89600 

400 

875 

870-93 

4-07 

850 

845-85 

413 

825 

820-78 

4-22 

800 

795-70 

4-30 

775 

770-59 

4-41 

750 

745-38 

4-52 

725 

720-36 

4-64 

700 

695-25 

4-75 

675 

670-27 

4-73 

650 

645-29 

4-71 

625 

620-30 

4-70 

600 

695-32 

4-68 

575 

570-32 

4-68 

550 

545-32 

4-68 

525 

520-32 

4-68 

500 

495-32 

4-68 

475 

470-50 

4-50 

450 

445-69 

4-31 

425 

420-87 

413 

400 

39605 

3-95 

375 

371-39 

3-61 

350 

346-73 

3-27 

325 

322-06 

2-94 

300 

297-40 

2-60 

275 

272-42 

2-58 

250 

247-44 

2-56 

225 

222-45 

2-55 

200 

197-47 

2-55 

175 

173-88 

2-12 

150 

148-30 

1-70 

125 

123-71 

1-29 

100 

9912 

0-88 

75 

74-34 

0-66 

50 

49-56 

0-44 

25 

24-78 

0-22 
















ASSAY PROPER OF SILVER BULLION. 


491 


Iliese numbers, however, are not constant, and vary with 
the circumstances under which the assays are made: two 
assays made from the same ingot, by the same assayer, can 
differ as much as four or five thousandths. Tillet has re¬ 
marked that the cupels can retain double as much silver as 
is lost; which proves, as has already been mentioned, that 
the silver obtained by cupellation is not perfectly pure, but 
may retain as much as 1 per cent, of lead. 

Special Instructions for the Assay of the Alloys of Silver 

and Copper. 

As before stated, peculiar weights are employed in the 
assay of silver bullion; and the silver assay pound, with its 
divisions, will be found described at page 31. 

In the 4 General Remarks on the Assay of the Alloys of 
Silver and Copper,’ it wall be seen that the alloy must be 
cupelled with a quantity of lead, varying with the amount 
of copper present in the alloy. Standard silver cupels very 
well with five times its weight of lead; but when the 
approximative quantity of alloy present is not known, it must 
be determined by a preliminary assay. 

Assay for Approximative Quantity of Alloy. —Weigh off 50 
grains of pure or test lead ; place them in a cupel previously 
made red-hot; when the lead is fused, and its surface 
covered with oxide, place in it by means of the light tongs 
(cq fig. 26, page 65)2 grains of the alloy under assay, wrapped 
in a small piece of thin paper. Allow the cupellation to go 
on according to the instructions, and with all the precautions 
already given, and when complete, weigh the resulting 
button, and, according to its weight, add lead in the actual 
assay in the quantity that is sufficient, as exhibited in the 
Table at page 488. 

Assay Proper of Silver Bidlion. —In this assay the ope¬ 
rator requires silver known to be standard, and pure lead. 
With the possession of the above substances the assay is 
thus proceeded with:—Place the 12 grains weight=1 lb., 
in the scale pan, and exactly counterbalance it with stan¬ 
dard silver. This is to serve as a check. Remove the 


492 


Til E ASSAY OF SILVER. 


weight, and in its place add so much of the alloy to be 
assayed that the balance is again equal. In one cupel, that 
destined to receive the check sample, place 60 grains of lead; 
and in another cupel place such a number of grains of lead 
as may be found necessary by the preliminary assay. When 
the lead in both cupels is fused, add the silver alloy, and 
cupel with the necessary precautions. When the buttons in 
the cupels are cold, seize them with the pliers, and if neces^ 
sary cleanse them with a hard brush, and place one in each 
balance pan. If they exactly balance each other, the alloy 
operated on is standard silver; if, however, it weighs less 
than the button produced from the check sample by the 
weight equivalent to 2 pennyweights, then it is 2 penny¬ 
weights worse than standard : on the other hand, if it be 
heavier by the same weight, it is 2 pennyweights better than 
standard. Silver is also reported as so much line : thus, 
standard silver may be reported as 11 ounces 2 penny¬ 
weights fine, and so on. In case extreme accuracy be 
required, correction must be made according to the standard 
as shown by the Table at page 490. The standard silver in 
England is fine. 

Assay of Alloys of Copper and Silver .—In the treatment 
on the large scale of copper ores containing silver, the con¬ 
tained silver is found alloyed with the copper, and it often 
falls under the assayer’s province to determine the quantity 
of precious metal. An assay of this kind is most conveni¬ 
ently accomplished by scorification before cupellation, thus : 
—Prepare four scorifiers ; weigh into each of them 50 grains 
of the alloy, 50 grains of fused borax, and 600 grains of 
lead, and proceed as already described under the head 
‘Assay of Ores of the First Class by Scorification.’ When 
the four buttons of lead are obtained, place them together 
in another scorifier, and submit to the furnace until the con¬ 
tents of the scorifier are completely covered with oxide; 
pour as usual, and cupel the resulting mass of lead. 

Alloys of Platinum and Silver .—If any substance con¬ 
taining platinum as well as silver were assayed as already 
described, the button resulting from the cupellation would, 
in addition to the silver, contain the whole of the platinum: 




SEPARATING SILVER FROM- THE BASER METALS. 


493 


In - such--a- case the button ' so obtained must be thus 
treated :— - 

If the alloy contain much platinum, it must be fused with 
twice its weight of silver ; then treated with hot nitric acid; 
evaporate the solution nearly to dryness ; add water and 
hydrochloric acid, until no further precipitation of silver as 
a white curdy precipitate (chloride of silver) takes place. 
The chloride of silver may be collected either on a filter or 
by decantation. The solution containing the platinum is 
treated with excess of sal-ammoniac solution until no further 
precipitation takes place; the solution evaporated to dry¬ 
ness. When cold, dilute alcohol is added; and the inso¬ 
luble yellow matter (ammonio-chloride of platinum) collected 
on a filter, washed with alcohol, dried, and ignited. The 
ignited residue is metallic platinum, which is weighed. The 
loss of weight which the alloy from cupel has sustained 
represents the amount of silver previously alloyed with it. 

." Alloy of Platinum , Silver , and Copper. —Treat such an 
alloy as above ; and the liquid, filtered from the ammonio- 
chloride of platinum, will contain the copper. Acidulate it 
with hydrochloric acid, add metallic zinc, and proceed as 
directed under the head 4 Humid Copper Assay.’ 

■ Native Silver , Hough Silver left on Sieve during Pulveri¬ 
sation of Silver Ores of First Class , and Native Alloys of 
Silver — as Antimonides , fc .—are treated by scorification 
and cupellation in precisely the same manner as just de¬ 
scribed for alloys of copper and silver. 

Dr. W. Dyce proposed, in 4 Tilloch’s Philosophical Maga¬ 
zine ’ for 1805, the following process for separating gold and 
silver from the baser metals :— 

4 Hitherto the process has always been, as far as I have 
understood it, attended with considerable difficulty in the 
execution ; but, by that which I am about to describe, is 
done with exact certainty. It was discovered and commu¬ 
nicated to me by a gentleman in the neighbourhood. The 
process consists in mixing not less than two parts of powdered 
manganese with the impure or compound metal, which 
should be previously flattened or spread out so as to expose 
as large a surface as possible, and broken or cut into small 


494 


THE ASSAY OF SILVER. 


pieces for the convenience of putting the whole into a cruci¬ 
ble, which is then to be kept in a sufficient heat for a short 
time. On removing the whole from the fire, and allowing it 
to cool, the mixture is found to be converted into a brownish 
powder, which powder or oxide is then to be mixed with 
an equal proportion of powdered glass, and then submitted 
in a crucible to a sufficient heat, so as to fuse the whole ; 
when the perfect metals are found at the bottom in a state 
of extreme purity, a circumstance of no small importance to 
the artist and the chemist, the latter of whom will find no 
difficulty in separating the one from the other with so little 
trouble compared with the usual processes, that I have no 
doubt it will always be practised in preference to the cupel/ 

Assay of Silver Bullion by the Wet Method .—From that 
which has been stated under the head of 4 Cupellation,’ it 
will be observed that there are many sources of error; such 
as volatilisation of the precious metal, its oxidation in the 
presence of excess of oxide of lead and atmospheric oxygen, 
and lastly, its absorption into the body of the cupel either as 
oxide or metal, or in both states. These losses, as before 
stated, vary with the temperature, the amount of lead em¬ 
ployed, and the texture of the cupel; and, as may be seen 
from the table of corrections as drawn up by D’Ar^et, give 
a very erroneous assay, unless the addition necessary for 
each standard be made. 

Considerable attention was called to this matter in France 
some years since, and a Special Commission was appointed 
to examine the subject thoroughly, and, if possible, to devise 
some means of assay which might be both easy and ac¬ 
curate. The result of this examination was the invention 
of a process of assay at once elegant and trustworthy : and 
as a full account of this method has not, to the authors 
knowledge, been translated and published in this country,* 
he has prepared the present from M. Gay-Lussac’s Report, 
which formed a part of a communication from M. Thiers to 
Earl Granville, and which appeared in the original language 
in the year 1837, in a Report on the Royal Mint. 

• Some portion of this report 1ms been published in Dr. lire’s Dictionary of 
Arts, Mines, and Manufactures. 


ASSAY OF SILYER BULLION' IN TIIE WET WAY. 


4f*5 


The new process of assay about to be described consists 
in determining the fineness of silver bullion by the quantity 
of a standard solution of common salt (NaCl) necessary to 
fully and exactly precipitate the silver contained in a known 
weight of alloy. This process is based on the following 
principles:— 

The alloy, previously dissolved in nitric acid (N0 5 ), is 
mixed with a standard solution of common salt, which pre¬ 
cipitates the silver as chloride, a compound perfectly inso¬ 
luble in water, and even in acids. 

The quantity of chloride of silver precipitated is deter¬ 
mined not by its weight, which would be less exact and 
occupy too much time, but by the weight or volume of the 
standard solution of common salt necessary to exactly pre¬ 
cipitate the silver previously dissolved in nitric acid. 

The term of complete precipitation of the silver can be 
readily recognised by the cessation of all cloudiness when 
the salt solution is gradually poured into that of the nitrate 
of silver. One milligramme of that metal is readily detected 
in 150 grammes of liquid ; and even a half or a quarter of a 
milligramme may be detected, if the liquid be perfectly 
bright before the addition of the salt solution. 

By violent agitation during a minute or two, the liquid, 
rendered milky by the precipitation of chloride of silver, 
becomes sufficiently bright after a few moments’ repose to 
allow of the effect of the addition of half of a milligramme 
of silver to be perceptible. Filtration of the liquid is more 
efficacious than agitation ; but the latter, which is much 
more rapid, generally suffices. The presence of copper, 
lead, or any other metal, with the exception of mercury 
(the presence of the latter metal requires a slight modifica¬ 
tion of the process, which will be hereafter pointed out), in 
the silver solution, has no sensible influence on the quantity 
of salt required for precipitation : in other words, the same 
quantity of silver, pure or alloyed, requires for its precipita¬ 
tion a constant quantity of the standard salt solution. 

Supposing that 1 gramme of pure silver be the quantity 
operated on, the solution of salt required to exactly precipi¬ 
tate the whole of the silver ought to be of such strength that. 


496 


THE ASSAY OF SILVER. 


if it be measured by weight, it shall weigh exactly 100 
grammes, or if by volume 100 cubic centimetres. This 
quantity of salt solution is divided into 1000 parts, called 
thousandths. 

The standard of an alloy of silver is generally the number 
of thousandths of solution of salt necessary to precipitate the 
silver contained in a gramme of the alloy. 

Measurement of the Solution of Common Salt. —The solu¬ 
tion of common salt will hereafter be termed the normal 
solution of common salt. It can be measured by weight or 
volume. The measure by weight gives greater precision, 
and it has the special advantage of being independent of 
temperature ; but it requires too much time in numerous 
assays. The measure by volume gives a sufficient exacti¬ 
tude, and requires much less time than the measure by 

weight; it is, indeed, liable to the influence 
of temperature, but tables for correction 
will be appended. 

Measure of the Normal Solution of Salt 
by Weight. —This solution should be so 
made that 100 grammes will exactly pre¬ 
cipitate 1 gramme of pure silver dissolved 
in nitric acid. In order to point out the 
method of taking the weight it must be 
supposed to have been previously pre¬ 
pared. After the process taking the weight 
is described, the mode of preparing the 
solution will be given. 

The solution is weighed in a burette 
(fig. 82), whose capacity is from 115 to 
120 grammes of the solution, and divided 
into grammes. These divisions are for 
the purpose of approximatively deter¬ 
mining the weight of solution, so as to 
shorten the operation of weighing. The 
burette is represented as closed by a 
cork, B , in order to prevent evaporation of the solution when 
the instrument is not in use. It is also easy to remedy the 
inconvenience of evaporation, by rinsing the burette with 









MEASUREMENT OF THE SOLUTION OF COMMON SALT. 497 

a small quantity of the fresh solution. On pouring the 
solution from the orifice, 0, of the burette, each division 
will furnish from 8 to 10 drops; and consequently the 
weight of a drop is about a decigramme. The burette is 
filled with solution to the division o ; it is then tared in 
a balance capable of turning with a centigramme. The 
burette is then removed, and its place supplied with a 
weight equivalent to the amount of solution required— 
100 grammes, for instance. The solution is then gradually 
poured from the burette into a bottle appointed for its 
reception, until the equilibrium is nearly established. It 
is not easy to attain the point exactly, as no smaller quan¬ 
tity than a drop can be poured from the burette. This, 
however, is a matter of indifference ; it suffices to know the 
exact weight of the solution poured out: suppose it to be 

99 gr. 85 c. : the mode of more nearly approximating the 
required weight of 100 grammes will now be pointed out. 

It must be remarked that it is not the amount of water 
contained in the 100 grammes that is of consequence, but 
only the quantity of salt found in solution ; this should 
exactly represent 1000 thousandths of pure silver. If near 

100 grammes of the normal solution be mixed 
with 900 grammes of water, it is evident that 
1 gramme of this new solution is equivalent to 
a decigramme of the first, and consequently it 
will be easy to obtain 100 grammes of the 
normal solution, or rather the 1000 thousandths 
of salt it ought to contain: it will now be suffi¬ 
cient to add to the 99 grammes already poured 
from the burette, 1^ grammes of the new solu¬ 
tion. It can be weighed, like the normal solu¬ 
tion, to a drop nearly, in the burette (fig. 83), 
of such a diameter that each small division repre¬ 
sents a decigramme of liquid, and consequently 
a centigramme of the normal solution ; but it 
is more readily measured by volume, preparing 
it in the manner to be hereafter pointed out. 
all confusion, a solution to be termed a clecime solution of 

salt is one containing the same quantity of salt 

K K 


Fig. 83. 



To avoid 


common 






498 


THE ASSAY OF SILVER. 


as the normal solution, in a weight or volume ten times 
greater. 

A decime solution of silver is a solution of silver equiva¬ 
lent to the latter, both mutually suffering complete decom¬ 
position. 

Preparation of the Decime Solution of Common Salt .— 
One hundred grammes of the normal solution of common 
salt are weighed in a flask (fig. 84) containing a kilogramme 
of pure water, when filled up to the mark a b , or 1000 
cubic centimetres ; this quantity is made up with pure water, 
taking care to agitate the whole well, to render the mixture 


Fig. 84. Fig. 85. 



homogeneous. A cubic centimetre of this solution repre¬ 
sents 1 thousandth of silver. This quantity is readily 
obtained by means of a pipette (fig. 85), gauged so that 
when filled up with water to the mark c d , it shall allow 1 
gramme, or 1 cubic centimetre, to run freely, the small 
quantity of liquid remaining in the pipette not forming part 
of the gramme. In pouring the liquid by drops, a little 
more or a little less than twenty may be counted, according 
to the size of the orifice, o. This number will not vary 
more than one drop. Half a cubic centimetre will con¬ 
sequently be represented by 10 drops, and a quarter by 5. 
The precision arrived at by this method of measurement 
suffices, since the possible error on the cubic centimetre will 
be but one-twentieth of that quantity, or one-twentieth of a 
thousandth ; if, however, many measures be required, then 
compensation must be made. 

















PREPARATION OF THE DECIME SOLUTION OF SILVER. 499 


1 lie decime solution ot common salt requisite for assays 
must be kept in a bottle (fig. 85) closed by a cork, traversed 
by the pipette firmly fixed in a hole 
bored for that purpose. To measure a 
thousandth with the pipette, the bottle 
is held with one hand, and the pipette 
with the other (fig. 86). The pipette 
is taken from the solution after its upper 
orifice has been closed by the fore¬ 
finger ; the lower orifice is then in¬ 
clined against the edge of the flask to 
remove the liquid, which without this 
precaution would remain there: the 
mark c d is then raised to the level of 
the eye, and by a suitable pressure of 
the forefinger on the upper orifice, 
which may be obtained by giving the pipette a slight 
alternating circular movement between the fingers, the 
solution is allowed to run out gradually. The instant the 
concave surface of the liquid is at the level c d , the pipette 
is firmly closed by pressure of the forefinger on its orifice, 
which is held above the bottle into which the solution is to 
be poured, and the forefinger removed so that it can be 
emptied. It is here necessary to remark, that in order to 
regulate the slow and regular runnings of the liquid from 
the pipette, by the pressure of the forefinger, the latter 
ought to be neither too moist nor too dry : if too dry it will 
not perfectly close the orifice, even by strong pressure; if 
too moist, it prevents the entrance of air, and the liquid will 
not run, or if it do, it will be irregularly. This observation 
should not be lost sight of in the use of the large burettes 
mentioned hereafter. 

Preparation of the Decime Solution of Silver .—The 
decime solution of silver is prepared by dissolving 1 gramme 
of pure silver in nitric acid, in a flask holding 1 litre (see 
fig. 84), and then diluting the solution with distilled water 
so that, cooled at the ordinary temperature of the air, it 
shall occupy exactly the volume of one litre. It is measured 
in precisely the same manner as the decime salt solution. 

K K 2 






500 


TTIE ASSAY OF SILVER. 


Weighing the Normal Solution of Common Salt .—To 
execute tins operation with rapidity, a balance similar to 
that represented at fig. 87 is employed. The arms are 
divided as in the assay balance described at p. 25 ; each of 
the arms, C B and C B , are furnished with a rider, c , of 
such a weight (about 5 decigrammes) that moved from the 


Fig. 87. 



right or the left of the centre <9, of each arm, it indicates 
two decigrammes. The space traversed by the rider is 
divided into twenty equal parts, representing an equal 
number of centigrammes. 

We will take for example the weighing of 100 grammes 
of normal solution of common salt, which is that most 
frequently made in the determination of the standard of all 
varieties of argentiferous matter. 

There are two weights, one, P , equal to the tare of the 
burette when full of solution to the mark o , the other, P', 
























PREPARATION OF T1IE NORMAL SALT SOLUTION. 


501 


equals 100 grammes. The burette is filled with solution, 
and placed on the right hand pan of the balance, on which 
it is kept in position by the collar d e, and through which it 
is passed before placing it on the pan. The tare, P, of the 
burette is supposed to be on the opposite side. If the equili¬ 
brium be not perfect, it is effected by the rider on the left; 
the burette is then removed, and 100 grammes of the solution 
(either more or less to one or two decigrammes) poured 
out. The burette is then again placed in the balance, with 
the 100 gramme weight P, the upper part of which is 
slightly concave, to receive the bottom of the burette, in 
order to prevent it sliding off. The equilibrium is again 
established by the aid of the rider on the right. If, for 
instance, it is found necessary to remove the rider 15 
divisions towards Vi, which represents 15 centigrammes, the 
weight of the solution poured out of the burette will be 
equal to 100 gr.—0*15 gr. = 99*85 gr. If, on the other 
hand, it is necessary to move the rider six divisions to¬ 
wards 6 7 , the weight of the solution will be 100 gr.+ 0 06 
gr. = 100 06 gr. 

The above method of weighing the salt solution appears 
to be the most convenient that can be employed, although 
it is not very expeditious. Other methods of weighing and 
measuring will be given in an appendix to this article. 

Preparation of the Normal Solution of Common Salt when 
measured by weight. —After having pointed out the method 
of weighing the normal solution of salt, and of taking very 
small quantities, its preparation will be described. 

Supposing the salt as well as the water to be employed 
are pure, the two substances have only to be taken in 
the following proportions :—0*5427 kilogrammes of salt 
and 99*4573 kilogrammes of water, to form 100 kilo¬ 
grammes of solution, of which 100 grammes will exactly 
precipitate 1 gramme of silver. But instead of pure salt 
which is difficult to procure, and which besides rapidly 
alters by the absorption of atmospheric moisture, it is 
preferable to employ a concentrated solution of commercial 
salt, which can be prepared in large quantities, and kept for 
use as needed. The quantity of salt it contains can be ascer- 



502 


THE ASSAY OF SILVER 


tained by evaporating a portion to dryness, and by a few 
experiments it is easy to determine in what proportion it 
shall be mixed with water to produce a solution, 100 grammes 
of which shall exactly precipitate 1 gramme of silver. 

Suppose, for example, that the salt solution contains 250 
grammes of salt per kilogramme, and that it is necessary to 
prepare 100 kilogrammes of the normal solution. Now, 
since for the preparation of this quantity 0*5427 kilo¬ 
grammes of pure salt is required, we have the following 
proportion:— 

0*250 : 1 : : 0*5427 : # = 2*1708 kilogs. 


Fig. 88. 


l\VV 


To this last weight enough water is added to make up 100 
kilogrammes, that is to say, 97*8292 kilogrammes, which 
quantity can be readily measured by means of 
a flask containing 5 or 6 kilogrammes pre¬ 
viously gauged. 

The mixture must be well agitated by 
means of the agitator (fig. 88), which is made 
of an ozier twig, split into four branches, to 
the extremities of which is attached a small 
square piece of silk. This substance is em¬ 
ployed to avoid the separation of filaments 
which would ensue from the use of any other 
material. This agitator can be introduced into 

very small openings, and is ex¬ 
ceedingly serviceable in agita¬ 
ting large masses of liquid. 

When well mixed, the solu¬ 
tion must be assayed. To effect 
this, dissolve 1 gramme of silver 
in nitric acid, sp. gr. 1*290, in a 
stoppered bottle (fig. 89) hold¬ 
ing about 200 grammes of water, 
tare the burette, fig. 82, filled 
with the solution, and pour rather more than less into the 
bottle, m pi opoi tion as the salt employed is impure, more 
than 100 grammes will be required to precipitate 1 gramme 
of silver. The mixture is at first milky, but, by vigorously 


Fig. 89. 








PREPARATION OF THE NORMAL SALT SOLUTION. 


503 


shaking the bottle, having its stopper firmly fixed, for about 
a minute, and then allowing it to remain at rest for a short 
time, the liquid will become perfectly bright; two drops of 
the solution must then be poured into it from the burette : 
if a cloudiness is produced, it is agitated again to brighten 
it, and two drops more added. This must be continued 
until the last two drops added give no precipitate. The 
operation is then terminated, and nothing remains to state 
but the result. 

Supposing the total weight of solution poured from the 
burette is 101*880 grammes, the last two drops must not 
be reckoned, because they produce no effect; the two pre¬ 
ceding drops were necessary, but in part only ; that is to 
say, that the number of drops to be deducted is less than 
four, and more than two, or rather that it is the mean term, 
three. Or the weight of a drop can be known exactly by 
taking that of a dozen : suppose it is equal to 0*082 gramme, 
three times that number must be deducted, or 10*255 
grammes from 10T880 grammes : there will remain 101*625 
grammes, representing the quantity of normal solution neces¬ 
sary to precipitate 1 gramme of silver. 

The solution is thus found to be too weak; to bring it to 
its proper standard it is necessary to remove 1*625 grammes 
of water from the 101*625 grammes of solution, or, what is 
the same thing, to add to the normal solution a certain 
quantity of the concentrated solution of common salt, which 
quantity may be found by the following proportion :— 

100 : 1*625 : : 2*1708 kilogrs. of silver solution : #=0*0353. 

After the addition of this quantity of salt to the normal 
solution, a fresh assay is made, proceeding in precisely the 
same manner as before; taking care, however, to pour from 
the burette a weight of solution slightly under 100 grammes, 
or 1000 decigrammes; for instance, 998*4 decigrammes, 
because it is not possible, in pouring the solution by drops, to 
arrive at the exact weight, 1000 decigrammes. To ascertain 
the true standard in the most exact manner possible, a 
decime solution must be prepared by weighing 100 
grammes of the normal solution, and diluting it with pure 


504 


THE ASSAY OF SILVER. 


water, so that it shall occupy one litre : a cubic centimetre 
of this solution will represent a decigramme of the normal 
solution. This decime solution will not be rigorously 
exact, since the normal solution has not been truly standar¬ 
dised ; but it is easily perceived that the error thus com¬ 
mitted is very small, and that it may be neglected. Neverthe¬ 
less, as soon as the normal solution is perfectly standardised, 
it is better to prepare another decime solution. 

A decime solution may be immediately obtained by dis¬ 
solving 0*5427 gramme of pure sea salt in such a quantity 
of water that the whole will occupy one litre ; yet the first 
process is preferable. 

. With the decime solution the assay may be thus con¬ 
tinued, remembering that the pipette described at fig. 83 
is a cubic centimetre containing 20 drops; that the half 
therefore is represented by 10 drops, and the fourth by 5. 

To the 998*4 decigrammes of normal solution already 
added, pour one pipette and 12 drops of the decime 
solution, which will exactly complete the weight of 1000 
decigrammes of normal solution. The mixture is agitated 
to brighten it, and one-thousandth of common salt or one 
pipette of the decime solution added. If this causes a 
cloudiness, it is agitated and a second thousandth added. 
This last should produce no opalescence. The weight of 
normal solution necessary to exactly precipitate one gramme 
of silver will be between 1000 and 1001 decigrammes; that 
is to say, the mean will be equal to 1000J. The standard 
of the normal solution is then too weak by half a thousandth ; 
to correct this a quantity of concentrated salt solution must 
be added equal to half a thousandth of that already added 
(2*1708 + 0*0353 = 2*2061 kilogrammes); that is to say, 
1*1 gramme. 

• A new assay is then made for verification. 

When the standard of a solution is very nearly arrived at, 
it is well to employ filtration to detect the slightest opales¬ 
cence, at least when sufficient time is not allowed for the 
liquid to become perfectly bright. The surest method, 
when the standard is nearly attained, is to place some of 
the liquid in two test glasses, and pour into one a few 


PRESERVATION OF TIIE NORMAL SALT SOLUTION. 


505 


drops of tlie decime solution of common salt, and into the 
other a corresponding number of drops of the decime 
solution of nitrate of silver. It may then be determined on 
which side the opalescence is manifested, and the assay of 
the normal solution may be continued after the mixture of 
the liquids in the two glasses, since the two quantities of 
the decime solutions of common salt and nitrate of silver 
mutually decompose each other, and do not interfere with 
the assay. Once the standard of the normal solution being 
definitely fixed, the sum of the quantities of the concentrated 
solution of common salt which have been employed, as well 
as those of the water, must be noted, and in the preparation 
of a new normal solution the proportions found as above 
would only have to be mixed to obtain at once a solution 
having very nearly its true standard. 

In determining the standard of the normal solution, sup¬ 
pose that it were always too weak, it would be necessary to 
add to the solution a certain quantity of common salt; but 
if the true amount had been exceeded, and it had been 
found too strong, the solution would have to be precipitated 
with the decime solution of silver ; and knowing the number 
of cubic centimetres or thousandths of silver which had 
been necessary to precipitate the excess of common salt, it 
could be determined what amount of water must be added 
to reduce the normal solution to standard. For instance, if 
2 thousandths of the decime solution of silver had been con¬ 
sumed, 2 thousandths of its weight of water would have to be 
added to the total amount of solution; that is to say, 02 
kilogramme or 200 grammes. 

Preservation of the Normal Solution of Common Salt .— 
The most suitable vessel for containing the normal solution 
of common salt is one of glass, because that cannot affect 
the standard. Large black glass bottles, termed carboys , 
are found in commerce. These bottles contain from 50 to 
60 litres, and are very applicable for this purpose. Fig. 90 
represents one of these bottles fixed in a stand formed of a 
sieve hoop. It is graduated into litres or kilogrammes of 
water, and a paper scale fixed on its side shows at any time 
the quantity of contained liquid. It is closed by an hydraulic 


506 


TIIE ASSAY OF SILVER. 




valve, made of sheet-iron, but the bell or cover is of glass- 
The detail of this valve is shown at fig. 91. The air can 

only enter the bottle by the narrow 
tube 1\ and cannot pass out by it; 
consequently, evaporation is not td 
be feared. The neck of the valve 
should be about a decimetre deep, 
into which mercury should be poured, 
but only to about one-third of its 
height. 

The solution is drawn from the 
bottle by the syphon S. This is 
furnished with a stopcock ; but this 
syphon being brittle, at least when 
not of metal, is not convenient in 
use, since it is incorporated with the 
bell of the valve: it is, therefore, 
preferable to pierce the bottom of the 
bottle (fig. 92), and fix a metal tube (T) by means of a plate 
moulded on the bottom, and cemented to it. This tube is 
raised a little above the bottom of the bottle, and covered by 


Fig. 92. 


Fig. 91. 


a small hoop, the object of which is to protect it from any of 
the mercury which might fall into it. It is terminated at its 
other extremity by a very narrow tube, so that the flow of 













































APPLICATION OF GAY-LUSSAC’S PROCESS. 


507 


the solution may not be too rapid. Hereafter a metal reser¬ 
voir will be described which has all the advantages of a glass 
vessel without its inconveniences. 

Application of the Process described in the Determination 
of the Standard of a Silver Alloy. —The alloy is supposed to 
be that made into coin, the mean standard of which is fixed 
at 900 thousandths, but which may vary from 897 to 903 
thousandths without ceasing to be legal (French standard 
for coin). One gramme is dissolved in the bottle (fig. 89) 
by about 10 grammes of nitric acid, sp. gr. 

1*290. This quantity of nitric acid can be 
readily taken by means of the pipette P 
(fig. 93), which contains 7*7 grammes of water 
to the mark a b. The solution may be 
accelerated by placing the bottle in a small 
saucepan of hot water, the bottom of which 
must be covered with a piece of cloth, so as 
to prevent contact of the glass and metal. 

The solution finished, and the flask slightly 
cooled, the nitrous vapour must be removed 
by a blower (see fig. 94), the nozzle of 
which is formed of a piece of bent glass tube, connected by 
a cork with a copper socket D, having a screw inside. This 
operation ought to be effected, as well as the solution of 
the alloy in nitric acid, under a chimney with 
a strong current of air, to carry off the nitrous 
vapour. 

The burette (fig. 82), being filled with the 
normal solution of common salt, and tared, 
about 90 grammes are poured into the solu¬ 
tion of the alloy; say 89*85 grammes. After 
agitating the liquor, a cubic centimetre of the 
decime solution of common salt is added, 
representing one thousandth of silver. If a 
cloudiness be observed, agitate again, and add 
a second thousandth of common salt, and so on, until 
the last thousandth gives no precipitate. Suppose it 
to be the fourth : that must not be counted, because it has 
produced no effect; and only half of the third must be 


Fig. 94. 











508 


TIIE ASSAY OF SILVER. 


taken, because only a portion of that was necessary. The 
standard of the alloy would be consequently equal to nearly 
half a thousandth, to 898*5 + 2*5 = 901. 

If it be desirable to approach still nearer to the true 
standard of the alloy, half-thousandths must be added until 
the last half thousandth gives no precipitate ; and in order 
to avoid all confusion, it is better to write with chalk on a 
black-board the thousandths of common salt, preceding 
them by the plus sign +, and on the other side the thou¬ 
sandths of nitrate of silver, preceding them by the sign — 
minus. 

In the above example, after the addition of the 4 thou¬ 
sandths of common salt, the last of which has produced no 
cloudiness, 1^ thousandths of nitrate of silver are added, 
which destroy 1^ thousandths of common salt, and brighten 
the liquid. If another half thousandth of nitrate of silver 
produce no precipitate, it is not taken into account, and is 
struck off from the table. From whence is concluded that 
the quantity of nitrate of silver necessary to destroy the 
excess of common salt is more than 1 and less than H ; 
that is to say, nearly the ^ of a thousandth, and is equal to 
1^. Thus the number of thousandths of salt really used is 
4 — 1*25 = 2*75. The standard of the alloy, therefore, is 
898*50+ 2*75 = 901*25. 

Another example, everything else remaining as above; 
but the first thousandth of salt did not precipitate. This is 
a proof that too much normal solution of common salt has 
been employed, and that there is an excess of salt in the 
liquid. Add one thousandth of silver, and agitate : things 
are now as at first, but it is nevertheless known that it is 
with nitrate of silver the process must be continued. One 
thousandth has been added, which produced a precipitate ; 
the second does not. The standard of the alloy is conse¬ 
quently 898*50-0*5 = 898. To approach still nearer to the 
real standard, destroy the last two thousandths of silver by 
two thousandths of common salt, and add half a thousandth 
of silver—a cloudiness is produced, as already known ; but 
another half thousandth does not precipitate. The standard 
of the alloy is therefore 898*50 —0*25 = 898*25. 


MEASURING THE NORMAL SOLUTION OF COMMON SALT. 509 


This process, on whicli it would be useless to enlarge 
further at present, because many other parts of the process 
to be presently described apply to it, is general, and gives 
exactly the standard of an alloy when it is known approxi¬ 
mative^, which can always be ascertained by a previous 
rough assay. 

ASSAY BY THE HUMID METHOD, MEASURING THE NORMAL 
SOLUTION OF COMMON SALT BY VOLUME. 

The measurement by weight of the normal solution of 
common salt has, as already stated, the advantage of being 
independent of temperature, of having the same degree of 
precision as the balance, and of requiring no correction. 
The measurement by volume has not all these advantages ; 
but, by ensuring an adequate amount of accuracy, it has 
that of being more rapid, and renders the new process* 
applicable to numerous and daily assays. 

The normal solution of common salt measured by volume 
is so prepared that it has a volume equal to that of 100 
grammes of water, or 100 cubic centimetres, and at a deter¬ 
minate temperature exactly precipitates 1 gramme of silver. 
The solution can be kept at a constant temperature, in 
which case the assay requires no correction; or, if the tem¬ 
perature be variable, its influence on the assay must be cor¬ 
rected. These two circumstances do not change the princi¬ 
ple of the process ; but they are sufficiently important to 
require some changes in the apparatus, and that each of the 
two processes should be treated separately: one, in which 
the normal temperature is constantly maintained; the other, 
in which it is variable. Experience has shown the latter to 
be preferable, and it will be first detailed ; the other will 
be described hereafter. 

Methods of Measurement in the employment of Volumes 
instead of Weights .—It will be here admitted, in pointing 
out the methods of measuring the normal solution of com¬ 
mon salt by volume, that it has been already prepared, and 
even, that it is kept at a constant temperature. It will after¬ 
wards be very easy to describe the method of preparation, 


510 


THE ASSAY OF SILVER. 


and give the corrections of which it is susceptible when its 
temperature varies. 

A volume of solution of 100 cubic centimetres is readily 
obtained by means of a pipette (fig. 95), graduated so that, 

Fig. 95. f,g. 96. filled with water to the 

mark a b , and the point or 
jet well wiped, it will allow 
LOO grammes of water, at a 
temperature of 15° (centi¬ 
grade), to flow in a continu¬ 
ous stream. A continuous 
stream is expressly men¬ 
tioned, because sometimes 
after the cessation of the jet 
the pipette will yet give two 
or three drops of liquid, 
which must not be counted. 
The weight of the volume 
of normal solution taken in 
this manner with suitable 
precautions will be constant, 
from one extreme to ano¬ 
ther, to centigrammes, 
or rather to ^th of a thou¬ 
sandth. 

The following is the most 
simple method of taking a measure of the normal solution 
of salt:— * 

Immerse the jet ( c ) of the pipette in the solution, apply 
the mouth to the upper orifice, and draw the liquid into u?, 
above the circular mark a b. Dexterously apply the fore¬ 
finger of one of the hands to this orifice, remove the pipette 
from the liquid, and hold it as represented at fig. 95. The 
mark a b is held on a level with the eye, and the surface of 
the solution allowed to descend until it forms a tangent 
with the plane a b. At this instant the jet ( c ) of the pipette 
is set at liberty by removing the finger against which it had 
been pressed, and, without otherwise changing the position 
of the hands, the contents are allowed to run into the bottle 





















MEASURING THE NORMAL SALT SOLUTION. 


511 



appropriated for that purpose, taking care to remove the 
pipette as soon as the steam stops. 

If, after having filled the pipette by aspiration, there is 
any difficulty found in a sufficiently rapid application of the 
forefinger to the superior orifice to prevent the fall of the 
liquid below the mark a b , the pipette must be removed 
from the liquid, the orifice being closed by pressing the 
tongue against it: then apply the middle finger of one of 


the hands to the lower orifice, remove the tongue, and 
apply the forefinger of the other hand to the larger orifice, 
previously wiped dry. 

The process just described for obtaining a measure of 
normal solution of salt is exceedingly simple, because it 
requires but little apparatus; but another, of more easy 


Fig. 98. 


Fig. 99. 


Fig. 97. 

































512 


THE ASSAY OF SILVER. 


execution, will now be mentioned, and which is at the same 
time more exact. 

In this process the pipette is filled from above, like a 
bottle, instead of by aspiration ; furthermore, it is a fixed 
apparatus. The figure 97 represents this apparatus. D U 
are two sockets, separated by a stopcock R. The upper 
one, which is screwed inside, is connected by means of a 
cork, Z, with the tube P, which conducts the solution of 
salt. The lower socket is cemented to the pipette ; it is 
furnished with an air-tap R\ and a screw V , which serves to 
regulate the admission of air into the pipette by a small 
opening provided for that purpose. Below the stopcock R', 
and soldered to the socket, is a very narrow silver tube IV, 
conducting the solution into the pipette, and allowing the 
escape of displaced air by the air-tap R'. The thumbscrews 
V' replace the ordinary screw, by means of which the key 
of the cock is adjusted on its seat. 

The figure 98 represents the above described apparatus 
on the other side. There will in this be noticed on the air- 
cock R ', an opening m, into which is ground by its ex¬ 
tremity Q the conical tube T (same figure). By this, air 
can be drawn out of the pipette whenever it is desirable to 
fill it from below. 

The pipette is carried by two horizontal arms, H K , fig. 
99. These arms are movable around a common axis A A , 
and are also capable of moving in the two longitudinal 
slots. 

They are fixed by two nuts, e e ', and their distance can 
be changed by means of pieces of wood or cork interposed, 
or even by the other nuts, o o'. In the upper arm, H, is a 
hole, in which is fixed by a wooden thumb-screw, t?, the 
socket of the pipette ; the corresponding hole of the lower 
arm is larger; the jet of the pipette is kept in position by a 
cork, L. The apparatus is fixed by its appendage, P, by 
means of a screw on an angle of the wall, or any other 
support. 

The method of filling this pipette is very simple: apply 
the forefinger of the left hand to the orifice, c, then open 
the two stopcocks, R , and R '; when the liquid nears the 


MEASURING THE NORMAL SOLUTION OF COMMON SALT. 513 


neck of the pipette its flow is moderated, and as soon as it 
is a little above the mark a 6, the stopcocks are shut, and 
the forefinger removed. The pipette must now be accurately 
adjusted, so that the liquid touches the mark a b , and none 
remains on the outside of the jet c. 

This last condition is easily fulfilled : after having removed 
the finger by which the orifice c of the pipette was closed, a 
moist sponge, m, fig. 100, enveloped in linen, is then applied, 
which absorbs the excess of liquid. To abridge the descrip¬ 
tion, this sponge will be termed ‘ the handkerchief,’ and 
the pipette is said to be clean when no liquid adheres ex¬ 
teriorly to the orifice. 

For convenience in use the handkerchief is forced into a 
tube of tin-plate, terminated by a little cup, open below, so 
that the liquid may run into the vessel (7, on which the 
tube is soldered : the liquid from the handkerchief is rejected : 

Fig. 100. Fig. 101. 




it can be easily removed to wash it, and if necessary it can 
be pushed towards the pipette by a small wedge of wood, o. 

At a later period the following mode of making the hand¬ 
kerchief has been found preferable : on a double iron wire 
(fig. 91) forming a spring, a small band of tin-plate t, is 
rolled; the iron wire is cemented into a tin-plate cylinder, 
closed on the lower end, and furnished on the upper with a 
border to convey the liquid which runs from the handkerchief 
in the vessel C. This cylinder passes into another soldered 













514 


THE ASSAY OF SILVER. 


to the bottom of the vessel, and can be kept in position by 
two projections o , which work in two slots cut in the other 
cylinder. 

To complete the adjustment of the pipette, the liquid 
must be made to fall to the level a b. To this end whilst 
the handkerchief is in contact with the jet of the pipette, 
air is allowed to enter slowly by unscrewing the screw v 
(fig. 99), and the instant the level is attained the handker¬ 
chief is removed, and the bottle F (fig. 100), which is 
employed to receive the solution, placed under the jet of the 
pipette. This must be accomplished rapidly, and without 
hesitation. The bottle is then placed in a cylinder of tin¬ 
plate, whose diameter is just a little larger, 
and which forms part and parcel of the 
vessel C, and the handkerchief. The whole 
of this apparatus has a sheet of tin-plate 
for a base movable between two wooden 
rods, R E , each having a slot in which the 
tin-plate moves. The extent of its move¬ 
ments is determined by two pieces of wood, 
b b , so placed that when it is stopped by 
them, the jet of the pipette corresponds to 
the centre of the neck of the bottle, or by 
the other in contact with the handkerchief. 
This arrangement is exceedingly handy for 
wiping and emptying the pipette, and has a 
sufficient amount of solidity to allow of its 
being removed and replaced without injury. 
It will be readily seen that when the admis¬ 
sion of air into the pipette has been once 
regulated by the screw v, it will be advan¬ 
tageous to leave it so, because the movement 
of the handkerchief or bottle can be so 
rapidly effected, that a drop of the liquid 
lias not time to accumulate and fall. 

Temperature of the Solution .—Having de¬ 
scribed the method of measuring the volume 
ot the normal solution of salt, that which appears the most 
suitable of obtaining the temperature will be pointed out. 







MEASURING TIIE NORMAL SALT SOLUTION. 


515 


The thermometer is placed in a glass tube, T (fig. 102), 
through which the solution passes, running into the pipette. 
It is suspended by a cork having four channels cut in it to 
allow the free passage of the liquid. The scale is engraved 
on the tube itself, and is repeated on the opposite side, so 
as to fix the eye by this double scale to the height of the 
thermometric column. The tube is fused at its lower end 
to a narrower tube, which is fixed by means of a cork into 
the socket of the stopcock of the pipette. The upper part 
of this tube is cemented to a socket of copper, tapped inside, 
which in its turn is fastened by a cock B , with the extremity 
(also tapped) of the tube T\ communicating with the reservoir 
of normal solution. The corks used as joints between the 
parts of the apparatus retain a certain amount of flexibility, 
and allow it being taken to pieces and put together again in 
a short space of time ; but it is essential to pass them into a 
hollow tube of glass or metal, to prevent them giving way 
under the pressure they have to sustain. If care be taken 
to coat them with a little tallow to stop the pores, no escape 
need be apprehended. 

Preservation of the Normal Solution of Salt in Metallic 
Vessels .—This subject has already been discussed, and it 
may appear unnecessary to again refer to it; but as it 
is here a question of metallic vessels, some details seem 
necessary. 

The figure 103 represents a cylindrical copper vessel, (7, 
holding about 110 litres. It is seen in section, Z, same 
figure. To its base is soldered a socket, to which is 
adapted a tube, with stopcock, T, through which the 
solution passes into the pipette; the upper part, which is 
slightly concave, having an opening closed by a screw 
stopper, i?, the edges of which press on a washer. This 
stopper is traversed by the tube £, which passes nearly to 
the bottom of the vessel, and through which air enters the 
apparatus, without the power of again passing out, so that 
evaporation is effectually prevented. This tube can be 
closed by a stopper, w, when the apparatus is not in use. 

The quantity of liquid contained in the vessel can be 
determined at any time by the aid of a wooden gauge, /, 

L L 2 


516 


THE ASSAY OP SILVER. 


graduated into litres. When used it is plunged vertically 
into the liquid, but is seldom needed. 

Pure or tinned copper alters in contact with the solution of 
salt and air, and the solution continually decreases in strength. 
This inconvenience is remedied by coating the inside of the 
cylinder with a soft cement, such as described at page 108 ; 
or with that cement softened by the addition of one-third 
its weight of yellow wax. This operation may be performed 


Fig. 103. 





by removing the tubes T and t , perfectly cleansing the 
inside of the cylinder, and heating it. About four or five 
pounds of the cement, made very hot, are run in, and the 
cylinder so turned round and inverted that the cement may 
run over every part. The turning is continued until the 
cement is cold. All the parts just described are united in 









PREPARATION OF THE NORMAL SALT SOLUTION. 


517 


the figure 103, forming a complete apparatus for the pre¬ 
servation of the normal solution of salt, for observing the 
temperature, and for measuring the volume. 

Preparation of the Normal Solution of Salt , measuring 
hxj Volume. —The preparation of the normal solution of 
salt, measured by volume, is much the same as of the 
solution measured by weight; there is, consequently, very 
little to add to that already given at pages 501-505, and to 
which the reader is referred. 

The cylinder, as already supposed, will contain about 
110 kilogrammes of water: no more, however, than 105 
are put in ; so that sufficient space may remain in order to 
agitate the fluid without throwing any out. According to 
the condition imposed, that 100 cubic centimetres, or one- 
tenth of a litre, of solution, should contain sufficient salt to 
completely precipitate 1 gramme of pure silver ; and further, 
admitting 13*516 for the equivalent of silver, and 7*335 
for that of salt, the quantity of pure salt to be dissolved in 105 
litres of water, and which corresponds to 105x10 = 1050 
grammes of silver, will be found by the following equa¬ 
tion :— 

13*516 : 7*335 : : 1050 gram. : x — 569*83 gram. 

And as the solution of commercial salt employed, page 501, 
contains approximative^ 250 grammes per kilogramme, 
2279*3 grammes of this solution will be required to furnish 
569*83 grammes of salt. As the 2279*3 grammes of solution 
contain 569*83 grammes of salt, it will consequently contain 
1709*5 grammes of water, which must be taken into account 
in measuring the 105 litres: that is no more than about 103*3 
must be employed. The whole being well mixed, the tubes 
and pipette must be washed out several times, by allowing 
the solution to run through them. The solution so passed 
is again placed in the cylinder, and after each addition the 
contents are well agitated, and lastly, the standard of the 
solution is determined, the temperature being supposed to 
remain constant. 

To accomplish this more readily, two decime solutions 
are prepared ; one of silver, and the other of salt. 


518 


THE ASSAY OF SILVER. 


The decime solution of silver, as already stated, is ob¬ 
tained by dissolving a gramme of silver in nitric acid, and 
diluting the solution with water until its volume is one 
litre. 

The decime solution of salt can be obtained by dissolving 
O'543 grammes of pure salt in water, so that the solution 
fills a measure of one litre ; but it is best prepared with the 
normal solution itself, which is to be standardised, by mixing 
one measure of the latter with nine measures of water. It 
must, however, be understood, that this solution is not 
rigorously equivalent to that of the silver, and only becomes 
so when the normal solution employed in its preparation 
becomes fixed at its true standard. If the normal solution 
be correct to ten thousandths, or one hundredth, the decime 
solution may be correct to the same degree. If ten 
thousandths of the latter solution be employed, the error 
committed will be one-tenth of a thousandth ; and only 
one hundredth when one thousandth is employed. Such 
errors may be entirely neglected ; nevertheless, after having 
exactly standardised the normal solution, it is better to 
prepare a new decime solution. 

After the preparation of the decime solutions, several 
bottles, as at fig. 89, must be prepared, each of which 
contains 1 gramme of pure silver dissolved in 8 or 10 
grammes of nitric acid. To these will be given the name 
of check, or witness-assays. 

To ascertain the standard of the normal solution pour a 
pipetteful into one of the check flasks, and agitate briskly 
until quite bright. After a few moments’ repose, two 
thousandths of the decime solution of salt are added, which, 
by superposition, will produce a precipitate. The normal 
solution is consequently too weak, since the salt employed 
was not perfectly pure. It is again agitated, and two other 
thousandths are added, which produce a precipitate. The 
addition of successive two thousandths is thus continued 
until the last produce no precipitate. Suppose in all six¬ 
teen thousandths have been added: the two last which 
have been added are not reckoned, as they produce no 
precipitate: the two preceding have only been in part 


PREPARATION OF THE NORMAL SOLUTION OF SALT. 519 


necessary; that is to say, that the acting thousandths 
added are above 12 and below 14, or, taking the mean, 
equal to 13. 

Thus in the existing state of the normal solution 1013 
parts are necessary to precipitate 1 gramme of silver, while 
only 1000 should be required. The quantity of concentrated 
solution of common salt to be added may be found by 
noting that the quantity of solution of common salt first 
employed—that is to say, 2279*3 grammes—has only 
produced a standard of 1000 —13 = 987 thousandths, and 
by the following equation :— 

987 : 2279*3 : : 13 : ^ = 30*02 grammes. 

This quantity of solution of common salt must, therefore, be 
mixed with the normal solution. 

After having washed the tubes and pipette with a new 
solution, another check gramme of silver is operated on. It 
is found, for instance, by proceeding but by one thousandths 
at a time, that the first precipitates, but the second does 
not. The standard of the solution is therefore too weak, 
being comprised between 1000 and 1001; that is to say, it 
is equal to 1000.^ : this, however, is not sufficiently near. 

Pour into the assay flask two thousandths of the decime 
solution of silver : these will merely decompose the two 
thousandths of salt, and the operation will have retrograded 
by two thousandths ; that is, it will be reduced to the point 
from which the thousandths were first employed. If, after 
brightening the liquor, half a thousandth of the decime 
solution is added, there will necessarily be a precipitate, as 
was before known ; but a second half thousandth produces 
no cloudiness. The standard of the normal liquid is 
therefore between 1000 and 1000£, or equal to 1000£. 

This for most purposes may be considered sufficiently 
near ; but if it be desirable to correct it, it may be remem¬ 
bered that the two quantities of solution of common salt 
added, 

2279*3 gr. + 30*02 gr. = 2309*32 gr. 

have only produced 999*75 thousandths, and that it is 
necessary to add a fresh quantity corresponding to the 




520 


THE ASSAY OF SILVER. 


quarter of a thousandth. The proportion is thus found:— 

999*75 : 2309*32 : : 0*25 : x. 

But as the first term only slightly differs from 1000, it is 

0*25 

necessary, in order to have x , to take^^ of 2309*32, and 

0*577 gr. will be found the quantity of solution of common 
salt to be added to the normal solution. It is not convenient 
to exactly take so small a quantity of solution of common salt 
by means of the balance, but is more readily attained in the 
following manner:— 

Weigh 50 grammes of the solution, and dilute with water 
until it occupies exactly half a litre, or 500 cubic centi¬ 
metres. A pipette of this solution, • containing a cubic 
centimetre, will give a decigramme of the original solution ; 
and as the pipette is divided into 20 drops, each drop will 
represent 5 milligrammes of the solution. Still smaller 
quantities may be determined by still further dilution, but 
greater precision is useless. 

The standardising of the normal solution is much less 
tedious than may be supposed ; and it must be remarked, 
that the liquid for a thousand assays is prepared at once, and 
moreover, that in preparing a fresh solution, its true standard 
may be very nearly obtained at once, if the quantities of 
water and salt solution previously employed have been 
noted. 

Correction of the Standard of the Normal Solution of Salt 
ivhen the Temperature varies .—It has been admitted that, in 
the determination of the standard of the normal solution of 
salt, the temperature has remained constant. Assays made 
under these circumstances need no correction; but if the 
temperature changes, the same measure of solution will not 
contain the same amount of salt. Supposing the solution of 
salt has been standardised at 15°. If, at the time an 
experiment is made, the temperature is 18°, for instance, 
the solution will be found too weak, since it has become 
expanded, and the pipette holds less than its weight. If, on 
the other hand, the temperature falls to 12°, the solution 
becomes concentrated, and is found too strong. It is there- 




CORRECTION OF THE STANDARD OF THE NORMAL SOLUTION. 521 


fore necessary to determine the correction to be made for 
any variation of temperature that may occur. 

To this end the temperature of a solution of common salt 
has been gradually raised from 0....5....10....15....20....25....30 
degrees, and three pipettefuls of the solution exactly weighed 
at each of the above temperatures. One-third of the total 
weight gives the mean weight of the contents of a pipette. 
The corresponding weights of a pipetteful of solution are 
then entered, and form the second column of the following 
table, called 4 Table of Correction for the Variations of 
Temperature in the Normal Solution of Salt.’ By this table 
correction may be made for any temperature between 0 and 
30 degrees, when the solution of salt has been standardised 
within the same limits. Suppose, for example, the solution 
had been standardised at 15°, and that at the time it was used 
its temperature was 18°. On referring to the second column 
of the table, it will be seen that the weight of a measure of 
solution at 15° is 100*099 gr.; and at 18° 100*065gr.; the 
difference 0*034 gr. is the quantity of solution taken too little, 
and consequently it must be added to the normal measure, so 
that it may be equal to one thousand thousandths. If the 
temperature of the solution had fallen to 10°, the difference 
of weight between a measure at 10° and a measure at 15° 
will be 0*019 gr., which must, on the contrary, be deducted 
from the measure, as it has been taken in excess. These 
differences of weight of a measure of solution at 15° and that 
of a measure for any other temperature, forms the column 
15° in the table, where they are expressed in thousandths. 
They are written on the same horizontal line as the tem¬ 
peratures to which each corresponds, with the sign + when 
they are to be added, and the sign - when to be subtracted. 
The columns 5°, 10°, 20°, 25°, 30° have been calculated in 
the same manner, to meet cases in which the normal solution 
had been graduated at each of the above-named temperatures. 
Thus, to calculate the column 10°, take the number 100*118 
from the column of weights as a point of departure, and 
find the difference for all the other numbers in the same 
column. 

An application of this table will be given hereafter. 


522 


TIIE ASSAY OF SILVER. 


Table of Correction for Variations in Temperature of the Normal 

Salt Solution. 


Temperature 

Weight 

5° 

10° 

15° 

20° 

25° 

30° 

Degrees 

Grammes 

Mill. 

Mill. 

Mill. 

Mm. 

Min. 

Mill. 

4 

100*109 

0*0 

—0*1 

+ 0*1 

4-0*7 

+ 1-7 

4-2*7 

5 

100*113 

0*0 

—0*1 

+ 0*1 

4-0*7 

+ 1-7 

4-2*8 

6 

100*115 

0*0 

0*0 

4-0*2 

4-0*8 

+ 1'7 

4-2*8 

7 

100*118 

+0*1 

00 

4-0*2 

4-0*8 

4-1*7 

42*8 

8 

100*120 

+0*1 

0*0 

4-0*2 

4-0*8 

4-1*8 

4-2*8 

9 

100*120 

+0*1 

00 

4-0*2 

4-0*8 

+ 1-8 

4-2*8 

10 

100*118 

+0*1 

0*0 

4-0*2 

4-0*8 

+ 1-7 

4-2*8 

11 

100*116 

0*0 

0*0 

4-0*2 

4-0*8 

+ 1-7 

4-2*8 

12 

100*114 

0*0 

0*0 

4-0*2 

4-0*8 

-Li-7 

4-2*8 

13 

100*110 

0*0 

—0*1 

4-0*1 

4-0*7 

+1-7 

42*7 

14 

100*106 

—0*1 

—0*1 

4-0*1 

4-0*7 

4-1*6 

4-2*7 

15 

100 099 

—0*1 

—0*2 

00 

4-0*6 

4-1*6 

4-2*6 

16 

100*090 

—0*2 

—0*3 

—0*1 

4-0*5 

4-1-5 

4-2*5 

17 

100*078 

—0*4 

—0*4 

—0*2 

4-0*4 

+ 1-3 

4-2*4 

18 

100*065 

—0*5 

—0*5 

—0*3 

4-0*3 

4-1*2 

4-2*3 

19 

100*053 

—0*6 

—0*7 

—0*5 

4-0*1 

4-1-1 

4-2*2 

20 

100*039 

—0*7 

—0*8 

—0*6 

0*0 

+ 1*0 

42*0 

21 

100*021 

—0*9 

—1*0 

—0*8 

—0*2 

4-0*8 

+ 1-9 

22 

100*001 

—1*1 

—1*2 

—1*0 

—0*4 

4-0*6 

+1-7 

23 

99*983 

—1*3 

-1*4 

—1*2 

—0*6 

4-0*4 

4-1*5 

24 

99*964 

—1*5 

—1*5 

—1*4 

—0*8 

4-0*2 

4-1-3 

25 

99944 

—1*7 

—1*7 

—1*6 

—1*0 

0*0 

4-l’l 

26 

99*924 

—1*9 

—1*9 

—1*8 

—1*2 

—0*2 

4-0*9 

27 

99*902 

—2*1 

—2*2 

—2*0 

—1*4 

—0*4 

40*7 

28 

99*879 

—2*3 

—2*4 

—2*2 

—1*6 

—0*7 

4-0*4 

29 

99*858 

—2.6 

—2*6 

—2*4 

—1*8 

—0*9 

4-0*2 

30 

99*836 

—2*8 

—2*8 

—26 

—2*0 

—1*1 

0*0 


TABLE FOR THE ASSAY, BY THE WET METHOD, OF AN ALLOY 
CONTAINING ANY PROPORTIONS WHATEVER OF SILVER, BY 
THE EMPLOYMENT OF A CONSTANT MEASURE OF THE NORMAL 
SOLUTION OF COMMON SALT. 

The process by which the normal solution of salt is 
measured by weight is applicable to the assay of every kind 
of alloy, since it suffices to take a weight of the solution 
corresponding to the presumed standard of the silver, and 
complete the assay by means of the decime solution ; the 
process by volume, however, has not the same advantage, 
because the volume of normal solution cannot be varied in 
the same manner as the weight. This inconvenience, how¬ 
ever, is of no very great consequence, for, by keeping the 
volume of normal solution constant, it suffices to vary the 
weight of the alloy, taking in each particular case a weight 


















EXPLANATION OF THE FOLLOWING TABLES. 


523 


which contains approximative^ one gramme of pure silver. 
Suppose the alloy has a standard of about 900 thousandths, 
we have the following proportion :— 

900 thousandths : 1000 of alloy :: 1000 thousandths : 

x = 1111 - 1 . 

If that weight be now taken to ascertain the standard of 
the alloy, it may be found, for instance, that to the measure 
of 1000 thousandths of salt it is yet necessary to add 4 thou¬ 
sandths of salt to precipitate the whole of the silver ; that is 
to say, that 1111*1 of alloy really contain 1004 of silver. 
From this result the real standard of the alloy may be found 
to be 903’6, by the following equation :— 

1111*1 : 1004:: 1000 : .£ = 903-6 

But such calculations, however simple, should be avoided 
where numerous daily assays are made, not only on account 
of the time consumed, but still more from the errors to 
which such operations are necessarily exposed. Fortunately, 
all these inconveniences may be avoided by the use of tables, 
which entirely free the assayer from calculation. 

Wishing in weighing the alloy to avoid fractions of thou¬ 
sandths, and only making use of tenths and half-tenths of 
thousandths, the weight of alloy increases, starting from a 
gramme, from 5 to 5 thousandths, and the corresponding 
standard for each of these weights has been sought, all con¬ 
taining one gramme of pure silver. Thus the weight 1020 
of alloy, in which there are 1000 of silver and 20 of copper, 
corresponds to the standard 980-39, obtained by the pro¬ 
portion— 

1020 : 1000:: 1000 : a? = 980*39 

On this principle are formed the first and second columns 
of the table marked Salt. The first contains the weight of 
each alloy, and the second its corresponding standard. The 
following columns, 1, 2, 3, to 10, give the standard of the 
alloy, when, instead of the 1000 milligrammes of silver it 
was supposed to contain, it really contained 1, 2, 3, &c. more, 
and consequently 1,2,3, &c. milligrammes of copper less. 

Another table, constructed in the same manner as the 
preceding, and marked Nitrate of Silver, gives the standard 


524 


TIIE ASSAY OF SILVER. 


of the alloy when, under the weight given in the first column, 
it contains 1, 2, 3, &c. milligrammes less silver, and as much 
more copper. Thus, for example, an alloy of the weight of 
1020 (1000 silver and 20 copper) has for its standard 980 4 
in both tables. If it always contains in the same weight 
4 more silver and consequently 4 less copper, its standard 
would be 984*3, and would be found in the 4 Salt ’ table at 
the intersection of the column 4, and the horizontal line 
1020. If, on the contrary, it contains 4 less of silver and 4 
more of copper, its standard will be 976*5, and will be found 
in the 4 Nitrate of Silver ’ table, at the intersection of the 
column 4, and the horizontal line 1020. 


TABLES 


FOR DETERMINING THE STANDARD OF ANY SILVER ALLOY 
BY EMPLOYING AN AMOUNT OF ALLOY ALWAYS 
APPROXIMATIVELY CONTAINING THE SAME 
AMOUNT OF SILVER. 


526 


ASSAY OF SILVER. 


Tables for Determining the Standard of any Silver 

approximately containing 


NITRATE OF 


Weight of 
Assay in 
Milligrs. 

0. 

l. 

1000 

1000-0 

999-0 

1005 

995-0 

994-0 

1010 

990-1 

989-1 

1015 

985-2 

984-2 

1020 

980-4 

979-4 

1025 

975-6 

974-6 

1030 

970-9 

969-9 

1035 

966-2 

965-2 

1040 

961-5 

960-6 

1045 

956-9 

956-0 

1050 

952-4 

951-4 

1055 

947-9 

946-9 

1060 

943-4 

942-4 

1065 

939-0 

938-0 

1070 

934-6 

933-6 

1075 

930-2 

929-3 

1080 

925-9 

925-0 

1085 

921-7 

920-7 

1090 

917-4 

916-5 

1095 

913-2 

912-3 

1100 

909-1 

908-2 

1105 

905-0 

904-1 

1110 

900-9 

900-0 

1115 

896-9 

896-0 

1120 

892-9 

892-0 

1125 

888-9 

888-0 

1130 

885-0 

884-1 

1135 

881-1 

880-2 

1140 

877-2 

876-3 

1145 

873-4 

872-5 

1150 

869-6 

868-7 

1155 

865-8 

864-9 

1160 

862-1 

861-2 

1165 

858-4 

857-5 

1170 

854-7 

853-8 

1175 

851-1 

850-2 

1180 

847-5 

846*6 

1185 

843-9 

843-0 


2 . 

3. 

4. 

998-0 

997-0 

996-0 

993-0 

992-0 

991-0 

988-1 

987-1 

986-1 

983-2 

982-3 

981-3 

978-4 

977-4 

976-5 

973-7 

972-7 

971-7 

968-9 

968-0 

967-0 

964-2 

963-3 

962-3 

959-6 

958-6 

957-7 

955-0 

954-1 

953-1 

950-5 

949-5 

948-6 

946-0 

945-0 

944*1 

941-5 

940-6 

939-6 

937-1 

936-1 

935-2 

932-7 

931-8 

930-8 

928-4 

927-4 

926*5 

924-1 

923-1 

922-2 

919-8 

918-9 

918-0 

915-6 

914-7 

913-8 

911-4 

910-5 

909-6 

907-3 

906-4 

905-4 

903-2 

902-3 

901*4 

899-1 

898-2 

897*3 

895-1 

894-2 

893-3 

891*1 

890-2 

889*3 

887-1 

886*2 

885*3 

883-2 

882-3 

881-4 

879-3 

878-4 

877-5 

875-4 

874-6 

873-7 

871-6 

870-7 

869*9 

867-8 

867-0 

866-1 

864*1 

863*2 

862*3 

860-3 

859*5 

858-6 

856-6 

855*8 

854-9 

853-0 

852*1 

851-3 

849-4 

848-5 

847-7 

845-8 

844-9 

844-1 

842-2 

841-3 

840-5 























ASSAY OF SILVER. 


527 


Alloy by employing an Amount of Alloy always 
the same Amount of Silver . 


SILVER. 


5. 

6 . 

7. 

8 . 

9. 

10 . 

995-0 

994-0 

993-0 

992-0 

991-0 

990-0 

990-0 

989-0 

988-1 

987-1 

986-1 

985-1 

985-1 

984-2 

983-2 

982-2 

981-2 

980-2 

980-8 

979-3 

978-3 

977-3 

976-4 

975-4 

975-5 

974-5 

973-5 

972-5 

971-6 

970-6 

970-7 

969-8 

968-8 

967-8 

966-8 

965-8 

966-0 

965-0 

964-1 

963-1 

962-1 

961-2 

961-3 

960-4 

959-4 

958-4 

957-5 

956-5 

956-7 

955-8 

954-8 

953-8 

952-9 

951-9 

952-1 

951-2 

950-2 

949-3 

948-3 

947-4 

947-6 

946-7 

945-7 

944-8 

943-8 

942-9 

943-1 

942-2 

941-2 

940-3 

939-3 

938*4 

938-7 

937-7 

936-8 

935-8 

934-9 

934-0 

934-3 

933-3 

932-4 

931-4 

930-5 

929-6 

929-9 

929-0 

928-0 

927-1 

926-2 

925-2 

925-6 

924-7 

923-7 

922-8 

921-9 

920-9 

921-3 

920-4 

919-4 

918-5 

917*6 

916-7 

917-0 

916-1 

915-2 

914-3 

913-4 

912-4 

912-8 

911-9 

911-0 

910-1 

909-2 

908-3 

908-7 

907-8 

906-8 

905-9 

905-0 

904-1 

904-5 

903-6 

902-7 

901-8 

900-9 

900-0 

900-4 

899-5 

898-6 

897-7 

896-8 

895-9 

896-4 

895-5 

894-6 

893-7 

892-8 

891-9 

892-4 

891-5 

890-6 

889-7 

888-8 

887-9 

888-4 

887-5 

886-6 

885-7 

884-8 

883-9 

884-4 

883-6 

882-7 

881-8 

880-9 

880-0 

880-5 

879-6 

878-8 

877-9 

877-0 

876-1 

876-7 

875-8 

874-9 

874-0 

873-1 

872-3 

872-8 

871-9 

871-0 

870-2 

869-3 

868-4 

869-0 

868-1 

867-2 

866-4 

865-5 

864-6 

865-2 

864-3 

863-5 

862-6 

861-7 

860-9 

861-5 

860-6 

859-7 

858-9 

858-0 

857-1 

857-8 

856-9 

856-0 

855-2 

854-3 

853-4 

854-1 

853-2 

852-4 

851-5 

850-6 

849-8 

850-4 

849-6 

848-7 

847-9 

847-0 

846-1 

846-8 

846-0 

845-1 

844-3 

843-4 

842-5 

843-2 

842-4 

841-5 

840-7 

839-8 

839-0 

839-7 

838-8 

838-0 

837-1 

836-3 

835-4 



















528 


ASSAY OF SILVER. 


NITRATE OF 


Weight of 
Assay in 
Milligrs. 

0. 

l. 

2. 

3. 

4. 

1190 

840*3 

849*5 

838*7 

837-8 

837*0 

1195 

836*8 

836*0 

835*1 

834*3 

833*5 

1200 

833*3 

832*5 

831*7 

830*8 

830*0 

1205 

829*9 

829*0 

828*2 

827*4 

826*6 

1210 

826*4 

825*6 

824*8 

824*0 

823*1 

1215 

823*0 

822*2 

821*4 

820*6 

819-7 

1220 

819*7 

818*8 

818*0 

817-2 

816*4 

1225 

816*3 

815*5 

814*7 

813*9 

813*1 

1230 

813*0 

812*2 

811*4 

810*6 

809*8 

1235 

809*7 

808*9 

808*1 

807*3 

806*5 

1240 

806*5 

805*6 

804*8 

804*0 

803*2 

1245 

803*2 

802*4 

801*6 

800*8 

800*0 

1250 

800*0 

799-2 

798-4 

797-6 

796*8 

1255 

796*8 

796*0 

795-2 

794*4 

793*6 

1260 

793*6 

792-9 

792*1 

791*3 

790*5 

1265 

790-5 

789-7 

788*9 

788*1 

787-3 

1270 

787-4 

786-6 

785-8 

785*0 

784*2 

1275 

784*3 

783*5 

782-7 

782*0 

781*2 

1280 

781*2 

780*5 

779-7 

778-9 

778-1 

1285 

778-2 

777-4 

776-6 

775-9 

775-1 

1290 

775-2 

774-4 

773-6 

772-9 

772-1 

1295 

772-2 

771-4 

770-7 

769-9 

769*1 

1300 

769*2 

768-5 

767-7 

766-9 

766-1 

1305 

766*3 

765-5 

764-7 

764-0 

763-2 

1310 

763-4 

762-6 

761*8 

761*1 

760-3 

1315 

760*5 

759*7 

758-9 

758*2 

757-4 

1320 

757-6 

756-8 

756*1 

755-3 

754-5 

1325 

754-7 

754-0 

753-2 

752*4 

751-7 

1330 

751*9 

751*1 

750-4 

749-6 

748-9 

1335 

749*1 

748*3 

747-6 

746-8 

746-1 

1340 

746*3 

745*5 

744-8 

744-0 

743*3 

1345 

743*5 

742-7 

742*0 

741*3 

740-5 

1350 

740-7 

740-0 

739*3 

738*5 

737-8 

1355 

738*0 

737-3 

736*5 

735*8 

735-1 

1360 

735*3 

734*6 

733*8 

733*1 

732-4 

1365 

732-6 

731-9 

731*1 

730*4 

729-7 

1370 

729-9 

729-2 

728-5 

727-7 

727*0 

1375 

727-3 

726-5 

725-8 

725*1 

724-4 

1380 

724-6 

723-9 

723*2 

722*5 

721*7 

1385 

722-0 

721*3 

720-6 

719*9 

719*1 

1390 

719*4 

718-7 

718-0 

717-3 

716-5 

1395 

716*8 

716*1 

715-4 

714-7 

714-0 

1400 

714*3 

713*6 

712*9 

712*1 

711*4 






















ASSAY OF SILVER. 


529 


SILV ER— continued. 


5. 

6. 

7. 

836*1 

835-3 

834-5 

832-6 

831-8 

831-0 

829-2 

828-3 

827-5 

825-7 

824-9 

824-1 

822-3 

821-5 

820-7 

818-9 

818-1 

817-3 

815-6 

814-7 

813-9 

812-2 

811-4 

810-6 

808-9 

808-1 

807-3 

805-7 

804*9 

804-0 

802-4 

801-6 

800-8 

799-2 

798-4 

797-6 

796-0 

795-2 

794-4 

792-8 

792-0 

791-2 

789-7 

788-9 

788-1 

786-6 

785-8 

785-0 

783-5 

782-7 

781-9 

780-4 

779-6 

778-8 

777-3 

776-6 

775-8 

774-3 

773-5 

772-8 

771-3 

770-5 

769-8 

768-3 

767-6 

• 766-8 

765-4 

764*6 

763-8 

762-4 

761-7 

760-9 

759-5 

758-8 

758-0 

756-6 

755-9 

755-1 

753-8 

753-0 

752-3 

750-9 

750-2 

749-4 

748-1 

747-4 

746-6 

745-3 

744-6 

743-8 

742-5 

741-8 

741-0 

739-8 

739-0 

738-3 

737-0 

736-3 

735-6 

734-3 

733-6 

732-8 

731-6 

730-9 

730-1 

728-9 

728-2 

727-5 

726-3 

725-5 

724-8 

723-6 

722-9 

722-2 

721-0 

720-3 

719-6 

718-4 

717-7 

717-0 

715-8 

715-1 

714-4 

713-3 

712-5 

711-8 

710-7 

710-0 

709-3 


8 . 

9. 

10 . 

833-6 

832-8 

831-9 

830-1 

829-3 

828-4 

826-7 

825-8 

825-0 

823-2 

822-4 

821-6 

819-8 

819-0 

818-2 

816-5 

815-6 

814-8 

813-1 

812-3 

811-5 

809-8 

809-0 

808-2 

806-5 

805-7 

804-9 

803-2 

802-4 

801-6 

800-0 

799-2 

798-4 

796-8 

796-0 

795-2 

793-6 

792-8 

792-0 

790-4 

789-6 

788-8 

787-3 

786-5 

785-7 

784-2 

783-4 

782-6 

781-1 

780-3 

779-5 

778-0 

777-3 

776-5 

775-0 

774-2 

773-4 

772-0 

771-2 

770-4 

769-0 

768*2 

767-4 

766-0 

765-2 

764-5 

763-1 

762-3 

761-5 

760-1 

759-4 

758-6 

757-2 

756-5 

755-7 

754*4 

753-6 

752-8 

751-5 

750-8 

750-0 

748-7 

747-9 

747-2 

745-9 

745-1 

744*4 

743-1 

742-3 

741-6 

740-3 

739-5 

738-8 

737-5 

736-8 

736-1 

734-8 

734-1 

733-3 

732-1 

731-4 

730-6 

729-4 

728-7 

727-9 

726-7 

726-0 

725-3 

724-1 

723-4 

722-6 

721-4 

720-7 

720-0 

718-8 

718-1 

717-4 

716-2 

715-5 

714-8 

713-7 

712-9 

712-2 

711-1 

710-4 

709-7 

708-6 

707-9 

707-1 


M M 


































530 


ASSAY OF SILVER. 


NITRATE OF 


Weight of 
Assay in 
Milligrs. 

0. 

l. 

1405 

711-7 

711-0 

1410 

709-2 

708-5 

1415 

706-7 

706-0 

1420 

704-2 

703-5 

1425 

701-8 

701-0 

1430 

699-3 

698-6 

1435 

696-9 

696-2 

1440 

694-4 

693-7 

1445 

692-0 

691-3 

1450 

689-7 

689-0 

1455 

687-3 

686-6 

1460 

684-9 

684-2 

1465 

682-6 

681-9 

1470 

680-3 

679-6 

1475 

678-0 

677-3 

1480 

675-7 

675-0 

1485 

673-4 

672-7 

1490 

671-1 

670-5 

1495 

668-9 

668-2 

1500 

666-7 

666-0 

1505 

664-5 

663-8 

1510 

662-3 

661*6 

1515 

660-1 

659-4 

1520 

657-9 

657-2 

1525 

655-7 

655-1 

1530 

653*6 

652-9 

1535 

651*5 

650-8 

1540 

649-4 

648-7 

1545 

647-2 

646-6 

1550 

645-2 

644-5 

1555 

643-1 

642-4 

1560 

641-0 

640-4 

1565 

639-0 

638-3 

1570 

636-9 

636-3 

1575 

634-9 

634-3 

1580 

632-9 

632-3 

1585 

630-9 

630-3 

1590 

628-9 

623-3 

1595 

627-0 

626-3 

1600 

625-0 

624-4 

1605 

623-1 

622-4 

1610 

621-1 

620-5 

1615 

619-2 

618-6 


2 . 

3. 

4. 

710-3 

709-6 

708-9 

707-8 

707-1 

706-4 

705-3 

704-6 

703-9 

702-8 

702-1 

701-4 

700-3 

699-6 

698-9 

697-9 

697-2 

696-5 

695-5 

694-8 

694-1 

693-1 

692-4 

691-7 

690-7 

690-0 

689-3 

688-3 

687-6 

686-9 

685-9 

685-2 

684-5 

683-6 

682-9 

682-2 

681-2 

680-6 

679-9 

678-9 

678-2 

677-5 

676-6 

675-9 

675-2 

674-3 

673-6 

673-0 

672-0 

671-4 

670-7 

669-8 

669-1 

668-5 

667-6 

666-9 

666-2 

665-3 

664-7 

664-0 

663-1 

662-5 

661-8 

660-9 

660-3 

659-6 

658-7 

658-1 

657-4 

656-6 

655-9 

655-3 

654-4 

653-8 

653-1 

652-3 

651-6 

651-0 

650-2 

649-5 

648-9 

648-0 

647-4 

646-7 

645-9 

645-3 

644-7 

643-9 

643-2 

642-6 

641-8 

641-2 

640-5 

639-7 

639-1 

638-5 

637-7 

637-1 

636-4 

635-7 

635-0 

634-4 

633-6 

633-0 

632-4 

631-6 

631-0 

630-4 

629-6 

629-0 

628-4 

627-7 

627-0 

626-4 

625-7 

625-1 

624*4 

623-7 

623-1 

622-5 

621-8 

621-2 

620-6 

619-9 

. 619-2 

618-6 

618-0 

617-3 

616-7 

































ASSAY OF SILVER. 


531 


• > ■ — - 

SILVER— continued. 


5. 

6. 

7. 

708-2 

707-5 

706-8 

705-7 

705-0 

704-3 

703-2 

702-5 

701-8 

700-7 

700-0 

699-3 

698-2 

697-5 

696-8 

695-8 

695-1 

694*4 

693-4 

692-7 

692-0 

691-0 

690-3 

689-6 

688-6 

687-9 

687-2 

686-2 

685-5 

684-8 

683-8 

683-2 

682-5 

681-5 

680-8 

680-1 

679-2 

678-5 

677-8 

676-9 

676-2 

675-5 

674-6 

673-9 

673-2 

672-3 

671-6 

670-9 

670-0 

669-4 

668-7 

667-8 

667-1 

666*4 

665*5 

664-9 

664-2 

663-3 

662-7 

662-0 

661-1 

660-5 

659-8 

658-9 

658-3 

657-6 

656-8 

656-1 

655-4 

654-6 

653-9 

653-3 

652-5 

651-8 

651-1 

650-3 

649-7 

649-0 

648-2 

647-6 

646-9 

646-1 

645-4 

644-8 

644-0 

643-4 

642-7 

641-9 

641-3 

640-6 

639-9 

639-2 

638-6 

637-8 

637-2 

636-5 

635-8 

635-1 

634-5 

633-8 

633-1 

632-5 

631-7 

631-1 

630-5 

629-7 

629-1 

628-5 

627-8 

627-1 

626-5 

625-8 

625-2 

624-5 

623-8 

623-2 

622-6 

621-9 

621-2 

620-6 

619-9 

619-3 

618-7 

618-0 

617-4 

616-8 

616-1 

615-5 

614-9 


8 . 

9 . 

10 . 

706-0 

705-3 

704-6 

703-5 

702-8 

702-1 

701-1 

700-3 

699-6 

698-6 

697-9 

697-2 

696-1 

695-4 

694-7 

693-7 

693-0 

692-3 

691-3 

690-6 

689-9 

688-9 

688-2 

687-5 

686-5 

685-8 

685-1 

684-1 

683-4 

682-8 

681-8 

681-1 

680-4 

679-4 

678-8 

678-1 

677-1 

676-4 

675-8 

674-8 

674-1 

673-5 

672-5 

671-9 

671-2 

670-3 

669-6 

668-9 

668-0 

667-3 

666-7 

665-8 

665-1 

664-4 

663-5 

662-9 

662-2 

661-3 

660-7 

660-0 

659-1 

658-5 

657-8 

656-9 

656-3 

655-6 

654-8 

654-1 

653-5 

652-6 

652-0 

651-3 

650-5 

649-8 

649-2 

648-4 

647-7 

647-1 

646-2 

645-6 

644-9 

644-2 

643-5 

642-9 

642-1 

641*4 

640-8 

640-0 

639-3 

638-7 

637*9 

637-3 

636-7 

635-9 

635-3 

634-6 

633-9 

633-2 

632-6 

631-8 

631-2 

630-6 

629-8 

629-2 

628-6 

627-8 

627-2 

626-6 

625-9 

625-2 

624-6 

623-9 

623-3 

622-6 

621-9 

621-3 

620-7 

620-0 

619-4 

618-7 

618-1 

617-4 

616-1 

616-1 

615-5 

614-9 

614-2 

613-6 

613-0 


M M 2 























532 


ASSAY OF SILVER. 


NITRATE OF 


Weight of 
Assay in 
Milligrs. 

0. 

l. 

2. 

3. 

4. 

1620 

617-3 

616-7 

616-0 

615-4 

614-8 

1625 

615-4 

614-8 

614-1 

613-5 

612-9 

1630 

613-5 

612-9 

612-3 

611-7 

611-0 

1635 

611-6 

611-0 

610-4 

609-8 

609-2 

1640 

609-8 

609-1 

608-5 

607-9 

607-3 

1645 

607-9 

607-3 

606-7 

606-1 

605-5 

1650 

606-1 

605-4 

604-8 

604-2 

603-6 

1655 

604-2 

603-6 

603-0 

602-4 

601-8 

1660 

602-4 

601-8 

601-2 

600-6 

600-0 

1665 

600-6 

600-0 

599-4 

598-8 

598-2 

1670 

598-8 

598-2 

597*6 

597-0 

596-4 

1675 

597-0 

596-4 

595-8 

595-2 

594-6 

1680 

595-2 

594-6 

594-0 

593-4 

592-9 

1685 

593-5 

592-9 

592-3 

591-7 

591-1 

1690 

591-7 

591-1 

590-5 

589-9 

589-3 

1695 

590-0 

589-4 

588-8 

588-2 

587-6 

1700 

588-2 

587-6 

587-1 

586-5 

585-9 

1705 

586-5 

585-9 

585-3 

584-7 

584-2 

1710 

584-8 

584-2 

583-6 

583-0 

582-5 

1715 

583-1 

582-5 

581-9 

581-3 

580-8 

1720 

581-4 

580-8 

580-2 

579-6 

579-1 

1725 

579-7 

679-1 

578-5 

578-0 

577-4 

1730 

578-0 

677-5 

576-9 

576-3 

575-7 

1735 

576-4 

575-8 

575-2 

574-6 

574-1 

1740 

574-7 

574-1 

573-6 

573-0 

572-4 

1745 

573-1 

572-5 

571-9 

571-3 

570-8 

1750 

571-4 

570-9 

570-3 

569-7 

569-1 

1755 

569-8 

569-2 

568-7 

568-1 

567-5 

1760 

568-2 

567-6 

567-0 

566-5 

565-9 

1765 

566-6 

566-0 

565-4 

564-9 

564-3 

1770 

565-0 

564-4 

563-8 

563-3 

562-7 

1775 

563-4 

562-8 

562-2 

561-7 

561-1 

1780 

561-8 

561-2 

560-7 

560-1 

559-5 

1785 

560-2 

559-7 

559-1 

558-5 

558-0 

1790 

558-7 

558-1 

557-5 

557-0 

556-4 

1795 

557-1 

556-5 

556-0 

555-4 

554-9 

1800 

555-6 

555-0 

554-4 

553-9 

553-3 

1805 

554-0 

553-5 

552*9 

552-3 

551-8 

1810 

552*5 

551-9 

551-4 

550-8 

550-3 

1815 

551-0 

550-4 

549-9 

549-3 

548-8 

1820 

549-4 

548-9 

548-3 

547-8 

547-2 

1825 

547-9 

547-4 

546-8 

546-3 

545-7 

1830 

546-4 

545-9 

545*4 

544-8 

544-3 





















ASSAY OF SILVER. 


533 




SILVER ,—con tinned. 


5 . 

6 . 

7 . 

8 . 

9 . 

10 . 

614-2 

613-6 

613-0 

612-3 

611-7 

611-1 

612-3 

611-7 

611-1 

610-5 

609-8 

609-2 

610-4 

609-8 

609-2 

608-6 

608-0 

607-4 

608-6 

607-9 

607-3 

606-7 

606-1 

605*5 

606-7 

606-1 

605-5 

604-9 

604-3 

603-7 

604-9 

604-3 

603-6 

603-0 

602-4 

601-8 

603-0 

602-4 

601-8 

601-2 

600-6 

600-0 

601-2 

600-6 

600-0 

599-4 

598-8 

598-2 

599-4 

598-8 

598-2 

597-6 

597-0 

596-4 

597-6 

597-0 

596-4 

595-8 

595-2 

594-6 

595-8 

595*2 

594-6 

594-0 

593-4 

592-8 

594-0 

593-4 

592-8 

592-2 

591-6 

591-0 

592-3 

591-7 

591-1 

590-5 

589-9 

589-3 

590-5 

589-9 

589-3 

588-7 

588-1 

587-5 

588-8 

588-2 

587-6 

587-0 

586-4 

585-8 

587-0 

586-4 

585-8 

585-2 

584-7 

584-1 

585-3 

584-7 

584-1 

583-5 

582-9 

582-3 

583-6 

583-0 

582-4 

581-8 

581-2 

580-6 

581-9 

581-3 

580-7 

580-1 

579-5 

578-9 

580-2 

579-6 

579-0 

578-4 

577-8 

577-3 

578-5 

577-9 

577-3 

576-7 

576-2 

575-6 

576-8 

576-2 

575-6 

575-1 

574-5 

573-9 

575-1 

574-6 

574-0 

573-4 

572-8 

572-2 

573-5 

572-9 

572-3 

571-8 

571-2 

570-6 

571-8 

571-3 

570-7 

570-1 

569-5 

569-0 

570-2 

569-6 

569-0 

568-5 

567-9 

567-3 

568-6 

568-0 

567-4 

566-9 

566-3 

565-7 

566-9 

566-4 

565-8 

565-2 

564-7 

564-1 

565-3 

564-8 

564-2 

563-6 

563-1 

562-5 

563-7 

563-2 

562-6 

562-0 

561-5 

560-9 

562-1 

561-6 

561-0 

560-4 

559-9 

559-3 

560-6 

560-0 

559*4 

558-9 

558-3 

557-7 

559-0 

558-4 

557-9 

557-3 

556-7 

556-2 

557-4 

556-9 

556-3 

555-7 

555-2 

554-6 

555-9 

555-3 

554-7 

554-2 

553-6 

553-1 

554-3 

553-8 

553-2 

552-6 

552-1 

551-5 

552-8 

552-2 

551-7 

551-1 

550-6 

550-0 

551-2 

550-7 

550-1 

549-6 

549-0 

548-5 

549-7 

549-2 

548-6 

548-1 

547-5 

547-0 

548-2 

547-7 

547-1 

546-6 

546-0 

545-5 

546-7 

546-2 

545-6 

545-1 

544-5 

544-0 

545-2 

544-7 

544-1 

543-6 

543-0 

542-5 

543-7 

543-2 

542-6 

542-1 

541-5 

541-0 



















534 

•% 


ASSAY OF SILVER 


NITRATE OF 


Weight of 
Assay in 
Milligrs. 

0. 

l. 

2. 

3. 

4. 

1835 

545-0 

544*4 

543-9 

543-3 

542-8 

1840 

543-5 

542-9 

542-4 

541-8 

541-3 

1845 

542-0 

541-5 

540-9 

540-4 

539-8 

1850 

540-5 

540-0 

539-5 

538-9 

538-4 

1855 

539-1 

538-5 

538-0 

537-5 

536-9 

1860 

537-6 

537-1 

536-6 

536-0 

535-5 

1865 

536-2 

535-7 

535-1 

534-6 

534-0 

1870 

534-8 

534-2 

533-7 

533-2 

532-6 

1875 

533-3 

532-8 

532-3 

531-7 

531-2 

1880 

531-9 

531-4 

530-8 

530-3 

529-8 

1885 

530-5 

530-0 

529-4 

528-9 

528-4 

1890 

529-1 

528-6 

528-0 

527-5 

527-0 

1895 

527-7 

527-2 

526-6 

526-1 

525-6 

1900 

526-3 

525-8 

525-3 

524-7 

524-2 

1905 

524-9 

524-4 

523-9 

523-4 

522-8 

1910 

523-6 

523-0 

522-5 

522-0 

521-5 

1915 

522-2 

521-7 

521-1 

520-6 

520-1 

1920 

520-8 

520-3 

519-8 

519-3 

518-7 

1925 

519-5 

519-0 

518-4 

517-9 

517-4 

1930 

518-1 

517-6 

517-1 

516-6 

516-1 

1935 

516-8 

516-3 

515-8 

515-2 

514-7 

1940 

515-5 

514-9 

514-4 

513-9 

513-4 

1945 

514-1 

513-6 

513-1 

512-6 

512-1 

1950 

512-8 

512-3 

511-8 

511-3 

510-8 

1955 

511-5 

511-0 

510-5 

510-0 

509-5 

1960 

510-2 

509-7 

509-2 

508-7 

508-2 

1965 

508-9 

508-4 

507-9 

507-4 

506-9 

1970 

507-6 

507-1 

506-6 

506-1 

505-6 

1975 

506-3 

505-8 

505-3 

504-8 

504-3 

1980 

505*0 

504-5 

504-0 

503-5 

503-0 

1985 

503-8 

503-3 

502-8 

502-3 

501-8 

1990 

502-5 

502-0 

501-5 

501-0 

500-5 

1995 

501-3 

500-7 

500-2 

499-7 

499-2 

2000 

500-0 

499-5 

499-0 

498-5 

498-0 





























ASSAY OF SILVER. 


535 


SILVER— continued. 


5 . 

6. 

7. 

8. 

9. 

10. 

542-2 

541-7 

541-1 

540-6 

540-0 

539-5 

540-8 

540-2 

539-7 

539-1 

538-6 

538-0 

539-3 

538-7 

538-2 

537-7 

537-1 

536-6 

537-8 

537-3 

536-8 

536-2 

535-7 

535-1 

536-4 

535-8 

535-3 

534-8 

534-2 

533-7 

534*9 

534-4 

533-9 

533-3 

532-8 

532-3 

533-5 

533-0 

532-4 

531-9 

531-4 

530-8 

532-1 

531-5 

531-0 

530-5 

529-9 

529-4 

530-7 

530-1 

529-6 

529-1 

528-5 

528-0 

529-3 

528-7 

528-2 

527-7 

527-1 

526-6 

527-8 

527-3 

526-8 

526-3 

525-7 

525-2 

526-5 

525-9 

525-4 

524-9 

524-3 

523-8 

525-1 

524-5 

524-0 

523-5 

523-0 

522-4 

523-7 

523-2 

522-6 

522-1 

521-6 

521-0 

522-3 

521-8 

521-3 

520-7 

520-2 

519-7 

520-9 

520-4 

519-9 

519-4 

518-8 

518-3 

519-6 

519-1 

518-5 

518-0 

517-5 

517-0 

518-2 

517-7 

517-2 

516-7 

516-1 

515-6 

516-9 

516-4 

515-8 

515-3 

514-8 

514-3 

515-5 

515-0 

514-5 

514-0 

513-5 

512-9 

514-2 

513-7 

513-2 

512*7 

512-1 

511-6 

512-9 

512-4 

511-9 

511-3 

510-8 

510-3 

511-6 

511-0 

510-5 

510-0 

509-5 

509-0 

510-3 

509-7 

509-2 

508-7 

508-2 

507-7 

508-9 

508-4 

507-9 

507-4 

506-9 

506-4 

507-6 

507-1 

506*6 

506-1 

505-6 

505-1 

506-4 

505-8 

505-3 

504-8 

504-3 

503-8 

505-1 

504-6 

504-1 

503-5 

503-0 

502-5 

503-8 

503-3 

502-8 

502*3 

501-8 

501-3 

502-5 

509-0 

501-5 

501-0 

500-5 

500-0 

501-3 

500-8 

500-2 

499-7 

499-2 

498-7 

500-0 

499-5 

499-0 

498-5 

498-0 

497-5 

498-7 

498-2 

497-7 

497-2 

496-7 

496-2 

497-5 

497-0 

496-5 

496-0 

495-5 

495-0 






















536 


ASSAY OF SILVER. 


Tables for Determining the Standard of any Silver 

approximately containing 


COMMON 


Weight of 
Assay in 
Milligrs. 

0 . 

i . 

2. 

3. 

4. 

1000 

1005 

1000-0 

995-0 

996-0 

997-0 

1 

998-0 

999-0 

1010 

990-1 

991-1 

992-1 

993-1 

994-1 

1015 

985-2 

986-2 

987-2 

988-2 

989-2 

1020 

980-4 

981-4 

982-4 

983-3 

984-3 

1025 

975-6 

976-0 

977-6 

978-5 

979-5 

1030 

970-9 

971-8 

972-8 

973-8 

974-8 

1035 

966-2 

967-1 

968-1 

969-1 

970-0 

1040 

961-5 

962-5 

963-5 

964-4 

965-4 

1045 

956-9 

957-9 

958-8 

959-8 

960-8 

1050 

952-4 

953-3 

954-3 

955-2 

956-2 

1055 

947-9 

948-8 

949-8 

950-7 

951-7 

1060 

943*4 

944-3 

945-3 

946-2 

947-2 

1065 

939-0 

939-9 

940-8 

941-8 

942-7 

1070 

934-6 

935-5 

936-4 

937-4 

938-3 

1075 

930-2 

931-2 

932-1 

933-0 

933-9 

1080 

925-9 

926-8 

927-8 

928-7 

929-6 

1085 

921-7 

922-6 

923-5 

924-4 

925-3 

1090 

917-4 

918-3 

919-3 

920-2 

921-1 

1095 

913-2 

914-2 

915-1 

916-0 

917-0 

1100 

909-1 

910-0 

910-9 

911-8 

912-7 

1105 

905-0 

905-9 

906-8 

907-7 

908-6 

1110 

900-9 

901-8 

902-7 

903-6 

904-5 

1115 

896-9 

897-8 

898-6 

899-5 

900-4 

1120 

892-9 

893-7 

894-6 

895-5 

896-4 

1125 

888-9 

889-8 

890-7 

891-6 

892-4 

1130 

885-0 

885-8 

886-7 

887-6 

888-5 

1135 

881-1 

881-9 

882-8 

883-7 

884-6 

1140 

877-2 

878-1 

878-9 

879-8 

880-7 

1145 

873-4 

874-2 

875-1 

876-0 

876-9 

1150 

869-6 

870-4 

871-3 

872-2 

873-0 

1155 

865-8 

866-7 

867-5 

868-4 

869-3 

1160 

862-1 

862-9 

863-8 

864-7 

865-5 

1165 

858-4 

859-2 

860-1 

860-9 

861-8 

1170 

854-7 

855-6 

856-4 

857-3 

858-1 

1175 

851-1 

851-9 

852-8 

853-6 

854-5 

1180 

847-5 

848-3 

849-2 

850-0 

850-8 

1185 

843-9 

844-7 

845-6 

846-4 

847-3 





























ASSAY OF SILVER. 


537 


Alloy by employing an Amount of Alloy always 
the same Amount of Silver. 


SALT. 


5. 

6. 

7. 

8. 

9. 

10. 

• 

1000*0 

995-0 

996-0 

997-0 

998-0 

999-0 

1000-0 

990-1 

991-1 

992-1 

993-1 

994-1 

995-1 

985-3 

986-3 

987-2 

988-2 

989-2 

990-2 

980-5 

981-5 

982-4 

983-4 

984-4 

985-4 

975-7 

976-7 

977-7 

978-6 

979-6 

980-6 

971-0 

972-0 

972-9 

973-9 

974-9 

975-8 

966-3 

967-3 

968-3 

969-2 

970-2 

971-1 

961-7 

962-7 

963-6 

964-6 

965-5 

966-5 

957-1 

958-1 

959-0 

960-0 

960-9 

961-9 

952-6 

953-5 

954-5 

955*4 

956-4 

957-3 

948-1 

949-1 

950-0 

950-9 

951-9 

952-8 

943-7 

944-6 

945-5 

946-5 

947-4 

948-4 

939-3 

940-2 

941-1 

942-1 

943-0 

943-9 

934-9 

935-8 

936-7 

937-7 

938-6 

939-5 

930-6 

931-5 

932-4 

933-3 

934-3 

935-2 

926-3 

927-2 

928-1 

929-0 

930-0 

930-9 

922-0 

922-9 

923-8 

924-8 

925-7 

926-6 

917-8 

918-7 

919-6 

920-5 

921-5 

922-4 

913-6 

914-5 

915-4 

916-4 

917-3 

918-2 

909-5 

910-4 

911-3 

912-2 

913-1 

914-0 

905-4 

906-3 

907-2 

908-1 

909-0 

909-9 

901-3 

902-2 

903-1 

904-0 

904-9 

905-8 

897-3 

898-2 

899-1 

900-0 

900-9 

901-8 

893-3 

894-2 

895-1 

896-0 

896-9 

897-8 

889-4 

890-3 

891-1 

892-0 

892-9 

893-8 

885-5 

886-3 

887-2 

888-1 

889-0 

889-9 

881-6 

882-5 

883-3 

884-2 

885-1 

886-0 

877-7 

878-6 

879-5 

880-3 

881-2 

882-1 

873-9 

874-8 

875-7 

876-5 

877-4 

878-3 

870-1 

871-0 

871-9 

872-7 

873-6 

874-5 

866-4 

867-2 

868-1 

869-0 

869-8 

870-7 

862-7 

863-5 

864-4 

865-2 

866-1 

866-9 

859-0 

859-8 

860-7 

861-5 

862-4 

863-2 

855-3 

856-2 

857-0 

857-9 

858-7 

859-6 

851-7 

852-5 

853-4 

854-2 

855-1 

855-9 

848-1 

848-9 

849-8 

850-6 

851-5 

852-3 



















538 


ASSAY OF SILVER. 


COMMON 


Weight of 
Assay in 
Milligrs. 

0. 

l. 

1190 

840*3 

841*2 

1195 

836*8 

837-7 

1200 

833*3 

834*2 

1205 

829*9 

830*7 

1210 

826*4 

827*3 

1215 

823*0 

823*9 

1220 

819-7 

820*5 

1225 

816*3 

817-1 

1230 

813*0 

813*8 

1235 

809-7 

810*5 

1240 

806*5 

807-3 

1245 

803*2 

804*0 

1250 

800*0 

800*8 

1255 

796*8 

797-6 

1260 

793*6 

794*4 

1265 

790-5 

791-3 

1270 

787-4 

788*2 

1275 

784-3 

785-1 

1280 

781*2 

782*0 

1285 

778-2 

779*0 

1290 

775-2 

776*0 

1295 

772-2 

773-0 

1300 

769-2 

770-0 

1305 

766*3 

767-0 

1310 

763-4 

764*1 

1315 

760-5 

761*2 

1320 

757-6 

758-3 

1325 

754-7 

755-5 

1330 

751-9 

752-6 

1335 

749-1 

749*8 

1340 

746-3 

747-0 

1345 

743*5 

744-2 

1350 

740-7 

741-5 

1355 

738*0 

738-7 

1360 

735-3 

736-0 

1365 

732-6 

733-3 

1370 

729-9 

730-7 

1375 

727-3 

728-0 

1380 

724-6 

725-4 

1385 

722*0 

722-7 

1390 

719*4 

720*1 

1395 

716-8 

717-6 

1400 

714*3 

715*0 


2. 

3. 

4. 

842*0 

842*9 

843-7 

838*5 

839*3 

840*2 

835*0 

835*8 

836*7 

831*5 

832*4 

833*2 

828*1 

828*9 

829*7 

824-7 

825*5 

826*3 

821*3 

822*1 

822*9 

818*0 

818*8 

819*6 

814*6 

815*4 

816*3 

811*3 

812*1 

813*0 

808*1 

808*9 

809*7 

804*8 

805*6 

806*4 

801*6 

802*4 

803*2 

798-4 

799-2 

800*0 

795-2 

796*0 

796*8 

792*1 

792*9 

793-7 

789*0 

789*8 

790*5 

785-9 

786-7 

787-4 

782-8 

783*6 

784-4 

779-8 

780-5 

781*3 

776-7 

777-5 

778-3 

773-7 

774-5 

775-3 

770-8 

771*5 

772-3 

767-8 

768-6 

769*3 

764*9 

765-6 

766-4 

762-0 

762-7 

763-5 

759-1 

759-8 

760*6 

756-2 

757-0 

757-7 

753*4 

754*1 

754*9 

750-6 

751-3 

752-1 

747-8 

748-5 

749-2 

745-0 

745-7 

746-5 

742-2 

743-0 

743-7 

739-5 

740*2 

741-0 

736-8 

737-5 

738-2 

734-1 

734-8 

735-5 

731*4 

732*1 

732-8 

728-7 

729-4 

730-2 

726-1 

726*8 

727-5 

723-5 

724-2 

724-9 

720-9 

721*6 

722*3 

718-3 

719*0 

719-7 

715-7 

716-4 

717-1 























ASSAY OF SILVER. 


539 


SALT.— continued . 

5. 

6. 

7. 

8. 

9. 

10. 

844-5 

845-4 

846-2 

847-1 

847-9 

848-7 

841-0 

841-8 

842-7 

843-5 

844-3 

845-2 

837-5 

838-3 

839-2 

840-0 

840-8 

841-7 

834-0 

834-8 

835-7 

836-5 

837-3 

838-2 

830-6 

831-4 

832-2 

833-1 

833-9 

834-7 

827-2 

828-0 

828-8 

829-6 

830-4 

831-3 

823-8 

824-6 

825-4 

826-2 

827-0 

827-9 

820-4 

821-2 

822-0 

822-9 

823-7 

824-5 

817-1 

817-9 

818-7 

819-5 

820-3 

821-1 

813-8 

814-6 

815-4 

816-2 

817-0 

817-8 

810-5 

811-3 

812-1 

812-9 

813-7 

814-5 

807-2 

808-0 

808-8 

809-6 

810-4 

811-2 

804-0 

804-8 

805-6 

806-4 

807-2 

808-0 

800-8 

801-6 

802-4 

803-2 

804-0 

804-8 

797-6 

798-4 

799-2 

800-0 

800-8 

801-6 

794-5 

795-3 

796-0 

796-8 

797-6 

798-4 

791-3 

792-1 

792-9 

793-7 

794-5 

795-3 

788-2 

789-0 

789-8 

790-6 

791-4 

792-2 

785-2 

786-0 

786-7 

787-5 

788-3 

789-1 

782-1 

782-9 

783-7 

784-4 

785-2 

786-0 

779-1 

779-8 

780-6 

781-4 

782-2 

782-9 

776-1 

776-8 

777*6 

778-4 

779-1 

779-9 

773-1 

773-8 

774-6 

775-4 

776-1 

776-9 

770-1 

770-9 

771-6 

772-4 

773-2 

773-9 

767-2 

767-9 

768-7 

769-5 

770-2 

771-0 

764-3 

765-0 

765-8 

766-5 

767-3 

768-1 

761-4 

762-1 

762-9 

763-6 

764-4 

765-2 

758-5 

759-2 

760-0 

760-7 

761-5 

762-3 

755-6 

756-4 

757-1 

757-9 

758-6 

759-4 

752-8 

753-6 

754-3 

755-1 

755-8 

756-6 

750-0 

750-7 

751-5 

752-2 

753-0 

753-7 

747-2 

748-0 

748-7 

749-4 

750-2 

750-9 

744-4 

745-2 

745-9 

746-7 

747-4 

748-1 

741-7 

742-4 

743-2 

743-9 

744-6 

745-4 

739-0 

739-7 

740-4 

741-2 

741-9 

742-6 

736-3 

737-0 

737-7 

738-5 

739-2 

739-9 

733-6 

734-3 

735-0 

735-8 

736-5 

737-2 

730-9 

731-6 

732-4 

733-2 

733-8 

734-5 

728-3 

729-0 

729-7 

730-4 

731-2 

731-9 

725-6 

726-3 

727-1 

727-8 

728-5 

729-2 

723-0 

723-7 

724-5 

725-2 

725-9 

726-6 

720-4 

721-1 

721-9 

722-6 

723-3 

724-0 

717-9 

718-6 

719-3 

720-0 

720-7 

721-4 

































510 


ASSAY OF SILVER. 


Weight of 
Assay in 
Miliigrs. 

0 . 

l . 

1405 

711-7 

712-5 

1410 

709-2 

709-9 

1415 

706-7 

707-4 

1420 

704-2 

704-9 

1425 

701-8 

702-5 

1430 

699-3 

700-0 

1435 

696-9 

697-6 

1440 

694-4 

695-1 

1445 

692-0 

692-7 

1450 

689-7 

690-3 

1455 

687-3 

688-0 

1460 

684-9 

685-6 

1465 

682-6 

683-3 

1470 

680-3 

680-9 

1475 

678-0 

678-6 

1480 

675-7 

676-3 

1485 

673-4 

674-1 

1490 

671-1 

671-8 

1495 

668-9 

669-6 

1500 

666-7 

667-3 

1505 

664-5 

665-1 

1510 

662-3 

662-9 

1515 

660-1 

660-7 

1520 

657-9 

658-5 

1525 

655-7 

656-4 

1530 

653-6 

654-2 

1535 

651-5 

652-1 

1540 

649-4 

650-0 

1545 

647-2 

647-9 

1550 

645-2 

645-8 

1555 

643-1 

643-7 

1560 

641-0 

641-7 

1505 

639-0 

639-6 

1570 

636-9 

637-6 

1575 

634-9 

635-6 

1580 

632-9 

633-5 

1585 

630-9 

631-5 

1590 

628-9 

629-6 

1595 

627-0 

627-6 

1600 

625-0 

625-6 

1605 

623-1 

623-7 

1610 

621-1 

621-7 

1615 

619-2 

619-8 


COMMON 


2. 

3. 

4. 

713-2 

713-9 

714-6 

710-6 

711-3 

712-1 

708-1 

708-8 

709-5 

705-6 

706-3 

707-0 

703-2 

703-9 

704-6 

700-7 

701-4 

702-1 

698-3 

698-9 

699-6 

695-8 

696-5 

697-2 

693-4 

694-1 

694-8 

691-0 

691-7 

692-4 

688-7 

689-3 

690-0 

686-3 

687-0 

687-7 

684-0 

684*6 

685-3 

681-6 

682-3 

683-0 

679-3 

680-0 

680-7 

677-0 

677-7 

678-4 

674-7 

675-4 

676-1 

672-5 

673-1 

673-8 

670-2 

670-9 

671-6 

668-0 

668-7 

669-3 

665-8 

666*4 

667-1 

663-6 

664*2 

664-9 

661-4 

662-0 

662-7 

659-2 

659-9 

660-5 

657-0 

657-7 

658-4 

654-9 

655-6 

656-2 

652-8 

653-4 

654-1 

650-6 

651-3 

651-9 

648-5 

649-2 

649-8 

646-4 

647-1 

647-7 

644-4 

645-0 

645-7 

642-3 

642-9 

643-6 

640-3 

640-9 

641-5 

638-2 

638-8 

639-5 

636-2 

636-8 

637-5 

634-2 

634*8 

635-4 

632-2 

632-8 

633-4 

630-2 

630-8 

631-4 

628-2 

628-8 

629-5 

626-2 

626-9 

627-5 

624-3 

624-9 

625-5 

622-4 

623-0 

623-6 

620-4 

621-0 

621-7 























ASSAY OF SILVER. 


541 



SALT— continued. 


5. 

6. 

7. 

8. 

9. 

10. 


715-3 

716-0 

716-7 

717-4 

718-1 

718-9 


712-8 

713-5 

714-2 

714-9 

715-6 

716-3 


710-2 

710-9 

711-7 

712-4 

713-1 

713-8 


707-7 

708-4 

709-2 

709-9 

710-6 

711-3 


705-3 

706-0 

706-7 

707-4 

708-1 

708-8 


702-8 

703-5 

704-2 

704-9 

705-6 

706-3 


700-3 

701-0 

701-7 

702-4 

703-1 

703-8 


697-9 

698-6 

699-3 

700-0 

700-7 

701-4 


695-5 

696-2 

696-9 

697-6 

698-3 

699-0 


693-1 

693-8 

694-5 

695-2 

695-9 

696-6 


690-7 

691-4 

692-1 

692-8 

693-5 

694-2 


688-4 

689-0 

689-7 

690-4 

691-1 

691-8 


686-0 

686-7 

687-4 

688-0 

688-7 

689-4 


683-7 

684-3 

685-0 

685-7 

686*4 

687-1 


681-4 

682-0 

682-7 

683-4 

684-1 

684-7 


679-1 

679-7 

680-4 

681-1 

681-8 

682-4 


676-8 

677-4 

678-1 

678-8 

679-5 

680-1 


674-5 

675-2 

675-8 

676-5 

677-2 

677-8 


672-2 

672-9 

673-6 

674-2 

674-9 

675-6 


670-0 

670-7 

671-3 

672-0 

672-7 

673-3 


667-8 

668-4 

669-1 

669-8 

670-4 

671-1 


665*6 

666*2 

666*9 

667-5 

668-2 

668-9 


663-4 

664-0 

664-7 

665-3 

666-0 

666-7 


661-2 

661-8 

662-5 

663-2 

663-8 

664-5 


659-0 

659-7 

660-3 

661-0 

661-6 

662-3 


656-9 

657*5 

658-2 

658-8 

659-5 

660-1 


654-7 

655*4 

656-0 

656-7 

657-8 

658-0 


652-6 

653-2 

653-9 

654-5 

655-2 

655-8 


650-5 

651-1 

651-8 

652-4 

653-1 

653-7 


648-4 

649-0 

649-7 

650-3 

651-0 

651-6 


646-3 

646-9 

647-6 

648-2 

648-9 

649-5 


644-2 

644-9 

645-5 

646-1 

646-8 

647-4 


642-2 

642-8 

643-4 

644-1 

644-7 

645-4 


640-1 

640-8 

641-4 

642-0 

642-7 

643-3 


638-1 

638-7 

639-4 

640-0 

640-6 

641-3 


636-1 

636-7 

637-3 

638-0 

638-6 

639-2 


634-1 

634-7 

635-3 

636-0 

636-6 

637-2 


632-1 

632-7 

633-3 

634-0 

634-6 

635-2 


630-1 

630-7 

631-3 

632-0 

632-6 

633-2 


628-1 

628-7 

629-4 

630-0 

630-6 

631-2 


626-2 

626-8 

627-4 

628-0 

628-7 

629-3 


624-2 

624-8 

625-5 

626-1 

626-7 

627-3 

1 

622-3 

622-9 

623-5 

624-1 

624-8 

625-4 


























542 


ASSAY OF SILVER. 


COMMON 


Weight of 
Assay in 
Milligrs. 

0. 

l. 

1620 

617-3 

617-9 

1625 

615-4 

616-0 

1630 

613-5 

614-1 

1635 

611-6 

612-2 

1640 

609-8 

610-4 

1645 

607-9 

608-5 

1650 

606-1 

606-7 

1655 

604-2 

604-8 

1660 

602-4 

603-0 

1665 

600-6 

601-2 

1670 

598-8 

699-4 

1675 

597-0 

597-6 

1680 

595-2 

595-8 

1685 

593-5 

594-1 

1690 

591-7 

592-3 

1695 

590-0 

590-6 

1700 

588-2 

588-8 

1705 

586-5 

587-1 

1710 

584-8 

585-4 

1715 

583-1 

583-7 

1720 

581-4 

582-0 

1725 

579-7 

580-3 

1730 

578-0 

578-6 

1735 

576-4 

576-9 

1740 

574-7 

575-3 

1745 

573-1 

573-6 

1750 

571-4 

572-0 

1755 

569-8 

570-4 

1760 

568-2 

568-7 

1765 

566-6 

567-1 

1770 

565-0 

565-5 

1775 

563-4 

563-9 

1780 

561-8 

562-4 

1785 

560-2 

560-8 

1790 

558-7 

559-2 

1795 

557-1 

557-7 

1800 

555-6 

556-1 

1805 

554-0 

554-6 

1810 

552-5 

553-0 

1815 

551-0 

551-5 

1820 

549-4 

550-0 

1825 

547-9 

548-5 

1830 

546-4 

547-0 


2. 

3. 

4. 

618-5 

619-1 

619-7 

616-6 

617-2 

617-8 

614-7 

615-3 

615-9 

612-8 

613-5 

614-1 

611-0 

611-6 

612-2 

609-1 

609-7 

610-3 

607-3 

607-9 

608-5 

605-4 

606-0 

606-6 

603-6 

604-2 

604-8 

601-8 

602-4 

603-0 

600-0 

600-6 

601-2 

598-2 

598-8 

599-4 

596-4 

597-0 

597-6 

594-7 

595-2 

595-8 

592-9 

593-5 

594-1 

591-1 

591-7 

592-3 

589-4 

590-0 

590-6 

587-7 

588-3 

588-9 

586-0 

586-5 

587-1 

584-3 

584-8 

585-4 

582-6 

583-1 

583-7 

580-9 

581-4 

582-0 

579-2 

579-8 

580-3 

577-5 

578-1 

578-7 

575-9 

576-4 

577-0 

574-2 

574-8 

575-4 

572-6 

573-1 

573-7 

570-9 

571-5 

572-1 

569-3 

569-9 

570-4 

567-7 

568-3 

568-8 

566-1 

566-7 

567-2 

564-5 

565*1 

565-6 

562-9 

563-5 

564-0 

561-3 

561-9 

562-5 

559-8 

560-3 

560-9 

558-2 

558-8 

559-3 

556-7 

557-2 

557-8 

555-1 

555-7 

556-2 

553-6 

554-1 

554-7 

552-1 

552-6 

553-2 

550-5 

551-1 

551-6 

549-0 

549-6 

550-1 

547-5 

548-1 

548-6 

















ASSAY OF SILVER. 


543 


SALT— continued. 


5. 

6. 

7. 

8. 

9. 

10. 

620-4 

621-0 

621-6 

622-2 

622-8 

623-5 

618-5 

619-1 

619-7 

620-3 

620-9 

621-5 

616-6 

617-2 

617-8 

618-4 

619-0 

619-6 

614-7 

615-3 

615-9 

616-5 

617-1 

617-7 

612-8 

613-4 

614-0 

614-6 

615-2 

615-8 

610-9 

611-5 

612-2 

612-8 

613-4 

614-0 

609-1 

609-7 

610-3 

610-9 

611-5 

612-1 

607-2 

607-8 

608-5 

609-1 

609-7 

610-3 

605-4 

606-0 

606-6 

607-2 

607-8 

608-4 

603-6 

604-2 

604-8 

605-4 

606-0 

606-6 

601-8 

602-4 

603-0 

603-6 

604-2 

604-8 

600-0 

600-6 

601-2 

601-8 

602-4 

603-0 

598*2 

598-8 

599-4 

600-0 

600-6 

601-2 

596-4 

597-0 

597-6 

598-2 

598-8 

599-4 

594-7 

595-3 

595-9 

596-4 

597-0 

597-6 

592-9 

593-5 

594-1 

594-7 

595-3 

595-9 

591-2 

591-8 

592-3 

592-9 

593-5 

594-1 

589-4 

590-0 

590-6 

591-2 

591-8 

592-4 

587-7 

588-3 

588-9 

589-5 

590-1 

590-6 

586-0 

586-6 

587-2 

587-8 

588-3 

588-9 

584-3 

584-9 

585-5 

586-0 

586-6 

587-2 

582-6 

583-2 

583-8 

584-3 

584-9 

585-5 

580-9 

581-5 

582-1 

582-7 

583-2 

583-8 

579-2 

579-8 

580-4 

581-0 

581-6 

582-1 

577-6 

578-2 

578-7 

579-3 

579-9 

580-5 

575-9 

576-5 

577-1 

577-6 

578-2 

578-8 

574-3 

574-9 

575-4 

576-0 

576-6 

577-1 

572-6 

573-2 

573-8 

574-4 

574-9 

575-5 

571-0 

571-6 

572-2 

572-7 

573-3 

573-9 

569-4 

570-0 

570-5 

571-1 

571-7 

572-2 

567-8 

568-4 

568-9 

569-5 

570-1 

570-6 

566-2 

566-8 

567-3 

567-9 

568-4 

569-0 

564-6 

565-2 

565-7 

566-3 

566-8 

567-4 

563-0 

563-6 

564-1 

564-7 

565-3 

565-8 

561-4 

562-0 

562-6 

563-1 

563-7 

564-2 

559-9 

560-4 

561-0 

561-6 

562-1 

562-7 

558-3 

558-9 

559-4 

560-0 

560*6 

561-1 

556-8 

557-3 

557-9 

558-4 

559-0 

559-6 

555-2 

555-8 

556-3 

556-9 

557-5 

558-0 

553-7 

554-3 

554-8 

555-4 

555-9 

556-5 

552-2 

552-7 

553-3 

553-8 

554-4 

554-9 

550-7 

551-2 

551-8 

552-3 

552-9 

553-4 

549-2 

549-7 

550-3 

550-8 

551-4 

551-9 




























544 


ASSAY OF SILVER. 


COMMON 


Weight of 
Assay in 
Milligrs. 

o. 

l. 

2. 

3. 

4. 

1835 

545*0 

545*5 

546*0 

546*6 

547*1 

1840 . 

543*5 

544*0 

544*6 

545*1 

545*6 

1845 

542*0 

542*5 

543*1 

543*6 

544*2 

1850 

540*5 

541*1 

541*6 

542 2 

542*7 

1855 

539*1 

539*6 

540*2 

540*7 

541*2 

1860 

537-6 

538*2 

538*7 

539*2 

539*8 

1865 

536*2 

536*7 

537*3 

637-8 

538*3 

1870 

534*8 

535*3 

535*8 

536*4 

536*9 

1875 

533*3 

533*9 

534*4 

534*9 

535*5 

1880 

531*9 

532*4 

533*0 

533*5 

534*0 

1885 

530*5 

531*0 

531*6 

532*1 

532*6 

1890 

529*1 

529-6 

530*2 

530*7 

531*2 

1895 

527-7 

528*2 

528*8 

529*3 

529*8 

1900 

526*3 

526*8 

527*4 

527*9 

528*4 

1905 

524*9 

525*4 

526*0 

526*5 

527*0 

1910 

523*6 

524*1 

524*6 

525*1 

525*6 

1915 

522*2 

522-7 

523*2 

523*8 

524*3 

1920 

520*8 

521*3 

521*9 

522*4 

522*9 

1925 

519*5 

520*0 

520*5 

521*0 

521*6 

1930 

518*1 

518*6 

519*2 

519*7 

520*2 

1935 

516*8 

517*3 

517*8 

518*3 

518*9 

1940 

515*5 

516*0 

516*5 

517-0 

517*5 

1945 

514*1 

514*6 

515*2 

515*7 

516*2 

1950 

512*8 

513*3 

513*8 

514*4 

514*9 

1955 

511*5 

512-0 

512*5 

513*0 

513*5 

1960 

510*2 

510*7 

511*2 

511*7 

512*2 

1965 

508*9 

509*4 

509*9 

510*4 

510*9 

1970 

507*6 

508*1 

508*6 

509*1 

509*6 

1975 

506*3 

506-8 

507*3 

507-8 

508*3 

1980 

505*0 

505*6 

506*1 

506*6 

507-1 

1985 

503*8 

504*3 

504*8 

505*3 

505-8 

1990 

502*5 

503*0 

503*5 

504*0 

504*5 

1995 

501*3 

501*8 

502*3 

502*8 

503*3 

2000 

500*0 

500*5 

501*0 

501*5 

502*0 
























ASSAY OF SILVER. 


,545 


SALT —con tin ucd. 


5. 

6. 

7. 

8. 

9. 

10 . 

547-7 

548-2 

548-8 

549-3 

549-9 

550-4 

546-2 

546-7 

547-3 

547-8 

548-4 

* 548*9 

544-7 

545-3 

545-8 

546-3 

546-9 

547-4 

543-2 

543-8 

544-3 

544-9 

545-4 

545-9 

541-8 

542-3 

542-9 

543-4 

543-9 

544-5 

540-3 

540-9 

541-4 

541-9 

542-5 

543-0 

538-9 

539-4 

539-9 

540-5 

541-0 

541-5 

537-4 

538-0 

538-5 

539-0 

539*6 

540-1 

536-0 

536-5 

537-1 

537-6 

538-1 

538-7 

534-6 

535-1 

535-6 

536-2 

536-7 

537-2 

533-2 

533-7 

534-2 

534-7 

535-3 

535-8 

531-7 

532-3 

532-8 

533-3 

533-9 

534-4 

530-3 

530-9 

531-4 

531-9 

532-4 

533-0 

528-9 

529-5 

530-0 

530-5 

531-0 

531-6 

527-6 

528-1 

528-6 

529-1 

529-7 

530-2 

526-2 

526-7 

527-2 

527-7 

528-3 

528-8 

524-8 

525-3 

525-8 

526-4 

526-9 

527-4 

523-4 

524-0 

524-5 

525-0 

525-5 

526-0 

522-1 

522-6 

523-1 

523-6 

524-2 

524-7 

520-7 

521-2 

521-8 

522-3 

522-8 

523-3 

519-4 

519-9 

520-4 

520-9 

521-4 

522-0 

518-0 

518-6 

519-1 

519-6 

520-1 

520-6 

516-7 

517-2 

517-7 

518-2 

518-8 

519-3 

515-4 

515-9 

516-4 

516-9 

517-4 

517-9 

514-1 

514-6 

515-1 

515-6 

516-1 

516-6 

512-8 

513-3 

513-8 

514-3 

514-8 

515-3 

511-4 

512-0 

512-5 

513-0 

513-5 

514-0 

510-1 

510-7 

511-2 

511-7 

512-2 

512-7 

508-9 

509-4 

509-9 

510-4 

510-9 

511-4 

507-6 

508-1 

508-6 

509-1 

509-6 

510-1 

506-3 

506-8 

507-3 

507-8 

508-3 

508-8 

505-0 

505-5 

506-0 

506-5 

507-0 

507-5 

503-8 

504-3 

504-8 

505-3 

505-8 

506-3 

502-5 

503-0 

503-5 

504-0 

504-5 

505-0 


N N 





























546 


THE ASSAY OF SILVER. 


APPLICATION. 

Assay of Pure , or nearly Pure , Silver , the Temperature of 
the Normal Solution of Salt being that at which it was 
standardised. 

First Example. —Let the ingot of silver have an approxi¬ 
mative standard of from 995 to 1000 thousandths. Take 
one gramme ; dissolve it in ten grammes of nitric acid, in 
the bottle, fig. 89. Then pour into the bottle an exact 
measure of the normal solution of salt, and brighten by agi¬ 
tation. The silver not being supposed to be quite pure, the 
standard is not further sought for by the decime solution of 
salt, but that of nitrate of silver is employed. 

One thousandth of this latter solution is poured into the 
bottle ; it becomes cloudy, and is well agitated. A second 
and a third thousandth also give a precipitate, but not so a 
fourth. From these data the following is the method of 
ascertaining the standard of the alloy :— 

The last thousandth of the decime solution of silver, 
having produced no cloudiness, is not to be counted. The 
third was necessary, but only partially so ; consequently the 
number of thousandths of silver necessary to decompose the 
excess of salt is more than 2 and less than 8 ; in other 
words, it is equal to the mean, 21 ; but since 2^ thousandths 
of silver have been required to complete the precipitation of 
salt representing 1000 thousandths of silver, it is evident 
that the silver submitted to assay contained 2 J- thousandths 
of alloy, and that its standard, to within nearly half a thou¬ 
sandth, is but 9974. 

If it be considered necessary to arrive nearer the true 

standard, the following proofs must be employed:_Pour 

into the solution li thousandths of salt, which will decom¬ 
pose a like number of thousandths of silver.* After due 

* It has already been stated how a thousandth of the decime solution may 
be subdivided by the number of drops furnished by the pipette. If, for 
instance, it contains 20 drops, 10 will give the half, 5 the quarter, &c. Half a 
thousandth may also be obtained by diluting the solution with its volume of 
water, and using a whole pipetteful. This latter plan has been found the best 
in practice. 


ASSAY OF PURE, OR NEARLY PURE, SILVER. 547 

agitation, add half a thousandth of nitrate of silver. Sup¬ 
posing a cloudiness is produced, no further addition must be 
made ; for it is already known that above the third thou¬ 
sandth no precipitate is formed in the liquid by nitrate of 
silver, and consequently only half of the last half thousandth 
must be calculated, as only a portion of it was necessary. 
From which, the entire number of thousandths of nitrate of 
silver being 4^, and those of salt 1J>, there remains 2| for 
the number of thousandths of nitrate of silver added to the 
normal solution ; and consequently the standard of the alloy 
is 1000 —2| = 997^. If, on the other hand, the last half 
thousandth of nitrate of silver had produced no cloudiness, 
it would not have to be reckoned, and only half of the pre¬ 
ceding half thousandth would have been taken. Thus from 
the 4 thousandths of nitrate of silver employed a quarter of 
a thousandth is deducted ; and from the difference, 3^, is 
yet deducted 14 of salt, the final remainder being thou¬ 
sandths of nitrate of silver which have been added to the 
normal solution : the standard of the alloy would be 1000 — 
2| = 997f. ' 

Although the above-described operation is very simple, 
yet it is desirable, in order to avoid all confusion, to note in 
writing such thousandths of salt or nitrate of silver as are 
added. The thousandths of salt indicating an increase of 
standard should be preceded by the sign + ; and the thou¬ 
sandths of nitrate of silver announcing a diminution of stan¬ 
dard, by the sign — . 

Second Example .—Suppose the ingot has a presumed 
standard of 895 thousandths, and the temperature of the 
normal solution supposed invariable. 

Find in the table of standards (Salt Table), first column, 
that which approaches the nearest to 895 ; it will be found 
to be 896’9, corresponding to the weight of 1115 milli¬ 
grammes. This weight of the alloy is taken and dissolved 
in nitric acid, a measure of normal solution of salt added, 
and the whole well agitated. The operator is, however, 
doubtful whether the assay must be proceeded with by the 
decirne salt solution, or the nitrate of silver decime solution. 
If the former produces a precipitate, it is gone on with; 


N N 2 



548 


THE ASSAY OF SILVER 


but if it does not precipitate, that already added is decom¬ 
posed by a similar addition of the second, and the solution 
rendered bright by agitation. A starting-point has now 
been arrived at for the continuance of the assay, for it is 
known that the nitrate of silver solution must be employed. 

Suppose, then, that the alloy, after the addition of the 
measure of normal solution, yet gives a precipitate with 
the decime solution of salt. The first 5 thousandths 
produce a precipitate, but not the sixth, which consequently 
is not counted. The fifth has only been partially required, 
so that it is more than 4 thousandths, and less than 5, or 
the mean, 4^, is the quantity required to entirely precipitate 
the excess of silver in the alloy submitted to assay. But by 
neglecting at first the fraction 0*5, seek in the Salt Table of 
Standards the number found on the longitudinal line of the 
weight 1115, under column 4; it is 900*4, and on adding 
0*5 to this number, we have 900*9, or 901, for the required 
standard. 

Supposing, however, that the same alloy, after the addition 
of the normal measure of salt, gives a precipitate with 
nitrate of silver, and that the 3 first thousandths produce 
a cloudiness, but not the fourth. The number of thousandths 
of nitrate of silver really necessary for complete precipitation 
will be very nearly 2|. To ascertain the real standard of 
the alloy of which 1115 thousandths were supposed to con¬ 
tain about 1000 thousandths of silver, take the number 
found in the horizontal line 1115, and in the column 2 of 
the Nitrate of Silver Table. This number, which is 895*1, 
diminished by the fraction 0*5, gives 894*6 for the standard 
of the alloy to within half a thousandth. 

Third Example .—The actual temperature of the normal 
solution of salt being 18° when it was standardised at 15°. 

The ingot of silver submitted to assay has an approxima¬ 
tive standard of 795 thousandths. Find in the Salt Table 
of Standards, first column, that which is nearest to it; it is 
793*7, corresponding to the weight 1260. This weight of 
the alloy is taken, and the operation proceeded with as 
already described. Supposing it had required 6*5 thou¬ 
sandths of salt to precipitate the whole of the silver contained 


GRADUATION OF THE NORMAL SOLUTION OF SALTS. 549 


in the alloy to within half a thousandth, the required stan¬ 
dard, without correction for temperature, will be 798*4 + 
0*4 = 798*8. But, making this correction, recourse must be 
had to the table, page 522, column 15 : the number 0*3, 
which will be found in the horizontal line 18 and the 
column 15, possesses the — sign; consequently it must be 
deducted from 798*8, and the remainder, 798*5, will be the 
standard weight. If the temperature of the solution, instead 
of being 3° higher than at the time it was standardised, was 
3° lower, or 12°, the correction must be added, and would 
be equal to +0*2. The standard of the 
alloy would consequently be 798*8 + 0*2 
= 799. 

Graduation of the Normal Solution of 

Salt , the Temperature being different to 

that at which it is wished to be graduated. 

Two equally ready processes can be 
employed. The one consists in reducing 
the temperature of the solution to the 
desired degree before standardising; the 
other, in determining its standard without 
regard to the temperature of the solution, 
and then correcting its influence by the 
aid of the tables of correction already 
given. 

First Process. —Place the liquid to be 
graduated in a bottle, I\ fig. 104. Intro¬ 
duce a thermometer, and heat to a deter¬ 
minate degree, say 20° for instance. This 
done, place the jet of the pipette in the 
bottle: raise the liquid by aspiration by 
means of the conical tube, r J\ fig. 98, 
which is adapted to the opening of the 
air-cock, II. As soon as the liquid is raised a little above 
the mark a b , which determines the capacity of the pipette, 
close the stopcock, and complete the measurement as usual. 
This same means of filling the pipette by aspiration may 





550 


THE ASSAY OF SILVER. 


be employed to fill it either with caustic alkali or nitric 
acid, as the case may be, to cleanse it instead of taking it 
to pieces. 

Second Method. —The solution of salt being supposed at a 
temperature of 16°, and it is desired to graduate it at that 
of 20°. Proceed with the standardising without regard to 
temperature ; but when it is obtained in each trial assay, it 
is necessary to make the correction required by the tem¬ 
perature. 

If, for example, in an approximative assay the standard of 
the solution was expressed by 1001*5, this standard would 
not only be too weak by 1*5 thousandth, but, according 
to the table of temperatures, by yet another 0*5, for the 
solution is weakened by this quantity by passing from 16° 
to 20°. The standard, if taken at this last temperature, 
would be too low by 2 thousandths, and "must consequently 
be corrected. 

If, on the other hand, the standard of the solution were 
too high instead of too low, and expressed by 998*5 at the 
temperature of 16°; at that of 20°, the solution being 
weakened by 0*5, the standard would only be but one 
thousandth too high, and it must be corrected by that 
quantity. 

Approximative Determination of the Standard of an 

Unknown Alloy. 

It has always been supposed, in the experiments already 
detailed, that the approximative standard of the alloy sub¬ 
mitted to assay was known: and this, indeed, is nearly 
always the case. If, however, this be unknown, two means 
are available for obtaining the necessary knowledge. A 
decigramme of the alloy is cupelled with one gramme of 
lead ; or, if it be desirable not to use the cupel, it may 
be ascertained by the humid method, in the following 
manner :— 

The assayer supposes the standard of the alloy known to 
about a twentieth, and it can always be found nearer than 
that by touch, densi ty, &c. A weight relative to its supposed 


MODES OF ABRIDGING MANIPULATION. 


551 


standard is taken, and its standard sought by adding the 
decime liquid by 10 thousandths at a time, by means of 
pipettes of this capacity (see fig. 105). The Fig - 105 - 
term of complete precipitation is soon passed, 
and the standard of the alloy to about 5 thou¬ 
sandths is thus ascertained. The approximate 
standard to 2^ thousandths may be obtained 
by adding only 5 thousandths of solution at a 
time. 

Suppose the alloy 840 thousandths. Take 
the weight 1190, corresponding to this standard, 
and proceed as in an ordinary assay, adding 
each time, for example, a pipette of 10 thou¬ 
sandths of salt solution. It is found the fifth 
pipette gives no precipitate, and consequently 
the number of thousands of salt for the precipi¬ 
tate of the silver to within 5 thousandths is 35. 

The 1199 of alloy will therefore contain 
1000 + 35 = 1035 of silver; and the approxi¬ 
mative standard will be obtained by the pro¬ 
portion— 

1120 : 1035:: 1000 : ^=869*7. 

Modes of Abridging Manipulation. 

In the statement already given of the mode of con¬ 
ducting the assay by the wet method, only such instructions 
have been given as were necessary for its full comprehen¬ 
sion, and everything that might call away or 
fatigue the attention has been omitted. Never¬ 
theless, here it will be convenient to describe 
some methods of abridging the necessary mani¬ 
pulations, supposing that ten, or at least five, 
assays are made at once. 

Bottles .—It is necessary to have these all, 
as nearly as possible, of the same height and 
diameter. They are marked progressively on the shoulder, 
as are also their stoppers (fig. 106), thus—1, 2, 3, 4 &c. 
They are taken successively by tens, in the natural order. 


Tig. 106 . 















552 


THE ASSAY OF SILVER. 


The stoppers are placed on a support, numbered in the same 
manner (fig. 107). The support is pierced with ten holes, 

distinguished in precedence by 
a mark between the fifth and 
sixth. 

Stand .—Each ten flasks are 
in turn placed in a case or stand 
of japanned tin-plate (fig. 108), having ten compartments 
numbered from 1 to 10. Each of these compartments is 
cut out anteriorly to about half their length, so as to 


allow the numbers of the bottles to be seen. The same 
stand serves for all the series, by making the same units 
correspond: thus No. 23 of the third series is placed in 

stand No. 3, &c. When each 
flask is charged with the 
alloy, about 10 grammes of 
nitric acid, 40° C., are mea¬ 
sured by a pipette (fig. 93) 
introduced into the bottles by 
means of a funnel with a large 
neck (fig. 109). The whole 
are then exposed to the heat 
of a water-bath, to facilitate 
the solution of the alloy. 

Water-bath .—This is an ob¬ 
long tin-plate vessel, calculated 
to receive 10 bottles (fig. 110). It has a movable double 
bottom, pierced with small holes, the principal object of 
which is to prevent the fracture of the bottles by isolating 


Fig. 110. 



Fig. 108. 



Fig. 109. 



Fig. 107. 
















MODES OF ABRIDGING MANIPULATION. 


553 


them from the bottom of the vessel, which is immediately 
exposed to the heat. On the movable bottom are soldered 
the cylinders c c, three or four centimetres in height, and 
above which, at the distance of eight centimetres, is a sheet 
of tin-plate, p p , pierced with ten holes, corresponding 
to the cylinders, and connected with the movable bottom 
by the supports, ss. These cylinders, and the sheet of 
tin-plate, are destined to isolate the bottles, F F, one from 
the other in the bath, and to keep them some time suspended 
over it, when the water is boiling, before complete im¬ 
mersion. The water-bath may be replaced by a steam- 
bath ; the bottles will then be supported by a grating above 
the surface of the water. The solution of the alloy in the 
nitric acid takes place rapidly, and as it gives rise to an 
abundant evolution of nitrous vapour, it must be made 
under a fine having a good draught. 

Flue .—This is represented at fig. Ill, C C is a flue 
resting on a table or support, T T, about 90 centimeters 
high. The anterior side in the 

O 

figure is removed to show the 
water-bath Z>, and the furnace F. 

The opening 0 of the flue is 
closed by the wooden door, p, 
movable on two excentric pivots, 
which keep it up during the 
solution, and allow it to fall so 
that the flask may be placed 
upon it. The nitrous vapour is 
removed from the bottles with the blower (fig. 94). The 
hood, //, prevents the diffusion of the nitrous vapour in 

the laboratory. 

Agitator.— Figure 112 gives a sufficiently exact idea of 
this apparatus, and dispenses with a long description. It 
has ten cylindrical compartments, numbered from 1 to 10. 
The bottles, after solution of the alloy, are placed in it in 
the order of their numbers. The agitator is then placed 
by the side of the pipette, by which is measured the normal 
solution of salt, and into each llask is poured a pipetteful 
of the solution. The bottles are fitted with their stopper, 


Fig. 111. 










554 


THE ASSAY OF SILVER. 


previously moistened with distilled water (fig. 113); they 
are then fixed in order with wooden wedges (fig. 114). 


Fig. 112. 


Fig. 113. 




Fig. 114. 



The agitator is suspended to a spring, Ji. and a rapid 
alternating movement given to it with both hands, by which 
the solution is agitated, and in less than a minute rendered 
as clear as water. This movement is assisted by a spiral 
spring, B, fixed to the agitator and its stand. The agitation 
finished, the wedges are removed, and placed in the vacant 
spaces between the compartments. The agitator is taken 
from the spring, and the bottles placed in order on a table 
prepared to receive them. 

Table .—This table (fig. 115) has a double bottom; the 
upper is pierced with ten holes, a little larger than the 
diameter of the bottles, and of such a distance from the 












MODES OF ABRIDGING MANIPULATION. 


555 


low oi poition, or false bottom, that the flasks do not rise 
abo\ e its edge, or at least but little. This disposition is to 


Fig. 115. 



protect the chloride of silver from the light, for it decom¬ 
poses in contact with water, and a little hydrochloric acid 
is produced, which requires for its precipitation a certain 
quantity of nitrate of silver, and so lowers the standard of 
the alloy. This cause of error is however not very great, at 
least when the light does not fall directly on the chloride ; 
but it is easy to avoid, and should not be neglected. The 
disposition already pointed out does not at all complicate 
the process, and is moreover useful, as it prevents the frac¬ 
ture or upsetting of the bottles. When but one bottle is 
operated on, it is placed for agitation in a japanned tin-plate 
cylinder, which is held as shown at fig. 116. On placing 
the bottles in their respective places on the table, a brisk 
circular movement is given to them, so as to remove any 
chloride of silver adhering to 
the sides ; their stoppers are 
removed and suspended by 
spring pincers, a a. These 
are formed of sheet-iron wire 
(see fig. 117). A thousandth 
of the decime solution is then poured into each bottle, and 
before this has been completed there will have formed in the 
first bottles where there is any precipitate, a well-marked 


Fig. 117. 









556 


TIIE ASSAY OF SILVER. 


nebular layer about a centimetre in thickness. At the back 
of the table is a black board, P P , divided into compart¬ 
ments numbered from 1 to 10, on each of which is marked 
with chalk the number of thousandths of decime liquid 
added to the contents of the corresponding bottle. The 
thousandths of salt announcing augmentation of standard 
are preceded by the sign + , those of nitrate of silver by the 
sign —. 

Lastly, the black board carries a small shelf pierced with 
holes, t t, and these receive the funnels or drain the bottles; 
on this shelf also are fastened the pincers for sustaining the 
stoppers. 

Cleansing the Bottles. —The assays terminated the liquid 
from each flask is poured into a large vessel in which there 
is always a slight excess of common salt, and when it is full 
the clear supernatant fluid is removed by means of a syphon. 
Immediately will be given the means of reducing the chloride 
of silver so collected to the metallic state. The bottles, to 
the number of ten, are first rinsed with the same water 
passed from one to the other, then a second, and then a third 
time with fresh water. They are then placed to drain on 

the board just mentioned, and the 
stoppers are placed in a stand by 
series of tens (see figs. 118 and 107). 
It is important to remark, that when 
a glass has been rinsed with distilled 
water, care must be taken not to 
rub it with the fingers, for water poured in such a vessel 
would always be clouded on the addition of nitrate of silver. 
This effect is due to the chlorides contained in the perspira¬ 
tion, and is of course more to be guarded against in summer. 

Reduction of Chloride of Silver, obtained in the Assay of 
Alloys by the Humid Method . 

Chloride of silver can be reduced without sensible loss, 
after having been well washed, by plunging into it scraps of 
iion oi zinc, and adding dilute sulphuric acid in sufficient 
quantity to set up a slight disengagement of hydrogen gas. 


Fig. 118 . 









PREPARATION OF PURE SILVER. 


557 


The whole can be left to itself, and in the course of a few 
days the silver is completely reduced. This point can be 
easily determined by the colour and nature of the product, 
but better still by treating a small quantity by ammonia, 
which, if the chloride is perfectly reduced, will give no 
precipitate or cloudiness on treatment with an acid. The 
chlorine remains in solution in the water combined with 
zinc or iron. The residue must now be washed; the first 
washings are made with acidulated water, to dissolve oxide 
of iron which might have formed, and the following with 
ordinary water: after having completed the washing as 
much water as may be left is decanted, the mass dried, and 
a little powdered borax added. Nothing now remains but 
to fuse it. The powdered silver being voluminous, it is 
placed by separate portions into the crucible, in proportion 
as it sinks. The heat should be at first moderate, but 
towards the end of the operation should be sufficiently high 
to reduce the silver and slag to a state of complete liquidity. 
If it be found that not quite all the chloride was reduced by 
the iron or zinc, a little carbonate of potash or soda may be 
added to the powdered silver. The standard of silver thus 
obtained is from 999 to 1000 thousandths. 

Preparation of Pure Silver. 

Take the silver prepared as above, dissolve it in nitric 
acid, and leave the solution some time in perfect rest in 
water, to deposit any gold it might contain. Decant the 
solution, and precipitate with common salt, well wash the 
precipitate, and reduce it, when the resulting silver will be 
pure. 

M. Gay Lussac here gives a description of a process for 
the precipitation of chlorine from nitric acid for use in the 
mode of assay already described; but as that acid in a state 
of purity forms an ordinary article of commerce, and can be 
obtained at most operative chemists, the process will not 
be here reproduced. 


558 


TIIE ASSAY OF SILVER. 


Modifications required in the Assay of Silver Alloys 

containing Mercury. 

Whenever mercury is present in solution with silver, it is 
thrown down as insoluble chloride, and the assay rendered 
inaccurate. The presence of mercury in silver can be 
readily detected by the remarkable change which occurs in 
chloride of silver on exposure to light (viz. blackening) 
when free from mercury ; but if the smallest quantity of the 
latter metal be present, no blackening will ensue. This 
source of error was removed by M. Levol in the following 
manner :—The sample being dissolved, as usual, in nitric 
acid, it was supersaturated with 25 cubic centimetres of 
caustic ammonia ; then add the pipetteful of normal solution, 
and supersaturate the excess of ammonia with 20 cubic 
centimetres of acetic acid, and the operation continued in 
the usual way. 

It may not be superfluous to state, that it is very easy to 
obtain an excellent result of an assay of silver containing 
mercury, made in the ordinary way, and in which the 
presence of the mercury is rendered manifest by the non¬ 
colouration of the precipitate under the influence of light. 
It suffices for this purpose to dissolve the precipitate in con¬ 
centrated ammonia, and to supersaturate with acetic acid. 

The ordinary acetic acid of commerce is employed, and 
the ammonia diluted with its volume of water, to avoid 
the too violent reaction. Both agents must be free from 
chlorides. 

Some little time after the publication of this, M. Gay 
Lussac examined the above process himself, and very con¬ 
siderably simplified it. He says : 4 After having confirmed 
by several experiments the accuracy of M. Levol’s process, 
I thought it might be simplified by adding to the nitric 
solution of silver the ammonia and acetic acid at one and 
the same time, but in sufficient quantity to saturate the 
whole of the nitric acid, both that in combination with the 
silver and that in the free state. Ten grammes of acetate 
of ammonia were added, with a little water, to the silver 
dissolved in nitric acid, and the assay finished in the ordinary 


APPARATUS FOR WEIGHING THE NORMAL SOLUTION OF SALT. 559 

manner. The quantity indicated by synthesis was found 
very accurately, although 100 thousandths of mercury 
had been added.’ Finally, M. Gay Lussac found that 10 
grammes of acetate of soda, in crystals, also fully answered 
the purpose ; and as that is a very cheap commercial salt, it 
is the best adapted for overcoming the difficulty in this class 
of assay, as regards the presence of mercury. 


APPENDIX. 

In the foregone description of the method of assay by the 
humid method, it has been the object of the writer not to 
distract the attention by too numerous details. Here, how¬ 
ever, will be given the processes to which 
personal experience has given the pre¬ 
ference. 

Apparatus for Weighing the Normal 
Solution of Salt. 

The apparatus about to be described 
enables the operator to weigh the normal 
solution of salt more rapidly than by 
means of the burette (fig. 82). It is a 
pipette, P (fig. 119), capable of furnishing 
in a continuous jet very nearly 100 
grammes of solution, when filled up to the 
mark a h , at the ordinary temperature. 

As this weight changes its volume with 
the temperature, some marks are traced 
on the neck of the pipette, so as to regu¬ 
late approximatively the volume to be 
taken. The pipette is terminated below 
by a three-footed stopcock, A, having 
a narrow outlet, p (about two millimetres). 

It is filled with solution by means of a small silver funnel 
(fig. 120), or better still by the suction tube, T, of the 
apparatus fig. 103, making an addition similar to that 
represented by fig. 118. The pipette is adjusted by ab- 


Fig. 119. 






560 


THE ASSAY OF SILVER. 


sorbing the excess of liquid with a small roll of filtering or 
other absorbent paper, or by allowing its exit by the 
stopcock. The following is the method of 
proceeding:— 

The pipette being approximative^ adjusted 
to nearly 1 or 3 thousandths, it is placed in the 
balance described, fig. 87, with a constant equi¬ 
valent weight, and the equilibrium effected by 
means of the rider. It is then placed over the 
bottle in which the assay was dissolved, the 
stopcock opened, and the liquid run out. Ihe 
stopcock must be shut as soon as the jet 
stops. The pipette is again placed in the balance with a 
weight of 100 grains, and the equilibrium effected by aid 
of the rider. This process is certainly more rapid than 
weighing with the burette. The weighing can be made 
even more rapidly by suspending the burette from the beam 
of the balance. 

Apparatus for Filling the Pipette with Normal Solution by 
Aspiration , and for convenient adjustment. 

This apparatus was the first employed, and has been in 
use for a considerable time. It is here described, because 
it appears extremely suitable for such persons as may be 
very little used to manipulation. It is sufficiently delineated 
in fig. 121. To fill the pipette, the jet or beak is plunged 
into a bottle containing the normal solution of salt, and the 
liquid is raised by the glass tube T, fixed to the socket D by 
means of a cork. The stopcock, 7?, is then closed whilst 
the tube is yet in the mouth, and the pipette is placed on 
its support in the following manner :—Take hold of its neck 
with the left hand, and place its beak or jet in the lower 
arm ; then its neck in the upper arm, the blades of which 
are opened by means of the fingers. The pipette thus 
placed, so that its jet cannot be injured by the bottle, F, 
which is destined to receive the solution, it is adjusted by 
aid of the screw, F, whilst the 6 handkerchief,’ d/, is applied 
to the jet; and as soon as it is adjusted, the handkerchief is 


Fig. 120. 






APPARATUS FOR FILLING THE 

removed with one hand, and the bottle placed u 
the other. The fluid is then allowed to run. 


Another Apparatus for filling the Pipette with Normal 

Salt Solution. 

In this apparatus (fig. 122) the pipette is movable from 
below, above, to receive the tube t, through which the salt 

Fig. 121. Fig. 122. 




solution passes, and which fits the neck of the pipette like a 
funnel. To obtain this ascensional movement without lateral 
deviation, the jet of the pipette passes into a hole pierced in 
the cross piece A B , and the stopcock, fitted to its upper 
part, carries two wings, R /?, working in slots cut in the 
supports, MM. The extent of movement is regulated by 
two corks, h b , cemented on to the lower part of the pipette. 

o o 

















THE ASSAY OF SILVER. 


562 


To fill it the forefinger of the left hand is placed against the 
lower orifice, and the whole raised until the cork, /q touches 
the cross piece. By this ascensional movement the tube, t , 
enters the neck of the pipette: immediately the stopcock 
of the reservoir must be opened. When the pipette is filled 
it is allowed to fall again, the stopcock shut, the finger 
removed, and the final adjustment made. 

The reservoir containing the solution is, for the sake of 
convenience, movable. 

Apparatus for Preserving the Normal Solution of Salt at 

a constant Temperature. 

The bulk of the normal solution of salt is too great to 
allow of its temperature being readily changed and reduced 
Fig. 123. to any determinate degree. This, 

indeed, would be useless, for it 
suffices that the quantity of solution 
to be employed in the day should 
possess the desired temperature. 

The solution, before entering 
the pipette from its reservoir, tra¬ 
verses an intermediate bottle, F 
(fig. 123), in which its tempera¬ 
ture is suitably varied. The flask 
has three tubulures, A, B , C. To 
the tubulure A is adapted a tube 
with a stopcock; this carries the 
solution into the bottle. To the 
tubulure B is fixed a centigrade 
thermometer, which indicates the 
temperature of the solution ; and 
through the tubulure C passes a 
syphon, which conveys the liquid 
to the pipette. The bottle is 
enveloped in a sheet-iron casing, 
(l e f g, whose diameter is from 
three to four centimetres greater. 
The intermediate space is closed 
above by a border on the envelope, and by strips of paper 





















MEANS OF PROTECTION FROM THE NITROUS VAPOUR. .563 


cemented with glue. The bottle stands on a plate of sheet- 
iron of its own diameter, fixed to the casing by three sup¬ 
ports ; but is separated by a thick sheet of card-board, 
employed as a bad conductor of heat. Below this plate, 
at the distance of from 12 to 15 millimetres, is another of 
smaller diameter, the object of which is to deaden and spread 
the too powerful heat of a spirit-lamp, //, or, what is better, 
a gas flame, which is employed to raise the temperature of 
the salt solution. The heated air rises into the annular 
chimney, between the bottle and its casing, and escapes by 
the small circular openings, h h , &c. This apparatus only 
serves to heat the solution : it is very difficult to cool it. 

Means of Protection from the Nitrous Vapour disengaged 

from the Bottles during the Process of Assay by the Humid 

Method. 

After the solution of the silver in nitric acid, it has been 
recommended that the nitrous vapour be expelled from the 
flasks by the introduction of air by the blower, fig. 94. 
But the solution yet remains impregnated with nitrous 
vapour which continues to pass off*; and it is only when it 
is completely cold that its disengagement is scarcely sensible. 
It therefore becomes necessary to find protection from this 
whilst the solution is yet very hot, and the vapour abundant. 
To the jet of the pipette, fig. 123, is adapted a funnel having 
a lateral tubulure, £, or simply an opening, by means of 
which it is placed in communication with a tube, 7", T 7 , of 
three or four centimetres in diameter, entering the case 77, 
in which is a lamp, or a chauffer with live coals. The air 
necessary to support this combustion can only enter the box 
by passing through the funnel, and carries off the nitrous 
vapour displaced by the normal solution at the moment it is 
run into the bottle. From the case the nitrous vapour 
escapes with the air, by the tube /?, either into a chimney or 
outside the laboratory. The funnel has a small portion cut 
off, so as to allow the free passage of the ‘ handkerchief ’ to 
the pipette. 

This apparatus is very handy, and answers its purpose 

o o 2 


504 


THE ASSAY OF SILVER. 


remarkably well; but, if the locality will allow, the follow¬ 
ing is preferable :— 

The jet of the pipette also has a funnel (see fig. 124), but 
the draught is determined from below by means of the tube 

T 7, which passes under the 
floor, and then enters the 
chimney or Hue under which 
the alloys are dissolved. The 
cylinder, e e , in which the 
bottle, F , is placed, is en¬ 
veloped in another cylinder, 
C C\ two centimetres greater 
in diameter. It is through 
this intermediate space that 
the nitrous vapour is carried 
off. But, so that none may 
remain in the funnel, air also passes in by four openings, 
o o , pierced through the cork by which the funnel is fixed 
to the pipette. Lastly, in order to render the funnel easy 
of ascent and descent, a ferrule, i r, furnished exteriorly 
with a screw thread, is cemented to the beak of the pipette ; 
and it is on this ferrule that the funnel turns. The interior 
cylinder is connected with the exterior by three small 
pieces of metal soldered to either cylinder, so as to leave the 
intermediate space as free as possible.* 


Fig. 121. 



Method of Talcing the Assay from the Ingot. 

The ingots are so rarely perfectly homogeneous, even 
taking as a starting-point the standard 950 thousandths, 
that the differences remarked between the assays of samples 
made in different places should rather be attributed to the 
above cause than to the assay itself. It is important, there¬ 
fore, to take a sample in a uniform manner, and from the 
same depth, on the upper surface of the ingot as on the 
lower. This condition is perfectly fulfilled by boring the 

A case built against the laboratory wall, having movable glazed windows 
in front, and connected with a Hue, is the most simple mode of promoting the 
escape of noxious vapours. 













METHOD OF TAKING THE ASSAY FROM THE INGOT. 565 

ingots with a kind of drill, similar to that employed by the 
smith, and which is represented at fig. 125. The ingot, Z, 
is placed in a copper tray, C ; 
and in order to retain the 
borings, which might other¬ 
wise be thrown out, the drill, 

/, is surrounded by a casing, 
m, which does not impede its 
motion, and stands freely on 
the ingot. After a few turns 
of the drill, the first borings, 
which are not pure, are re¬ 
moved by means of a feather, 
and only those following are 
collected and reserved for 
assay. If it be desirable to 
try the lateral faces, it is 
necessary to employ a pressure 
screw, to keep the ingot in the 
position that may be deemed 
necessary. 

The following is a slight 
modification of the process as 
already described, and the 
necessary apparatus are to be found in every laboratory. 
In this class of assay very simple apparatus are employed 
(similar to those used in alkalimetry) to determine the 
weight of the standard solution of salt added : and the 
results so obtained always correspond. 

The apparatus employed are as follows :—A small flask 
for the solution of the silver to be assayed, a stoppered 
bottle (containing from three to four fluid ounces), in which 
the decomposition of the silver solution is made, and two 
small alkalimeters, known by the name of Schuster’s. The 
alkalimeter is a light glass bottle, with two openings, one of 
which is drawn out, and extends over the side of the flask, 
parallel to its bottom ; this aperture is for the purpose of 
allowing the fluid contained in the bottle to pass out in 
single drops, which it does most effectually. The other 


Fig. 125. 





566 


THE ASSAY OF SILVER. 


aperture just mentioned is furnished with a small stopper, 


and is used for the introduction of the fluid. An accurate 


balance and weights, with a few stirring rods, complete the set. 

The standard solution of salt is made as follows:—It is 
absolutely necessary to employ pure salt. It is better to 
manufacture this, which may be accomplished by accurately 
neutralising pure hydrochloric acid with bicarbonate ot 
soda,-evaporating the solution to dryness, and fusing the 
dry residue, taking care to place it, whilst warm, in a well- 
stopped bottle, to preserve it perfectly free from moisture. 

Distilled water must also be employed, of which 94*573 
parts must have added to them 5*427 parts of salt, as above 
prepared. The solution so formed must be kept in glass 
stoppered bottles, and exposed as little as possible to the 
air during manipulation, otherwise it will become sensibly 
stronger by evaporation, and cause fallacious results; 100 
grains, by weight, of this solution, precipitate exactly 10 
grains of silver. 

Another solution is also employed, the use of which will be 
pointed out hereafter. This solution is made by dissolving 
10 grains of pure silver in a small quantity of nitric acid, 
and adding pure water (distilled) to the solution, until its 
weight amounts to 10,000 grains. This is the verifying 
solution. 

This solution must be preserved with the same precautions 
as to exposure to air, &c., as the last; in addition to which 
it must be kept in a dark place. 

The assay is thus made : 10 grains of the alloy are dis¬ 
solved in nitric acid; when the solution is effected, water 
(distilled) must be added, and the whole poured into the 
assay bottle before mentioned. The flask in which the 
solution was made must be carefully washed out, and the 
rinsings added to that already in the assay bottle. A quan¬ 
tity (any amount) of the solution of salt must be placed in 
one of the alkalimeters, which, with it, must be carefully 
weighed, and the weight noted. The standard solution is 
now to be added, drop by drop, to the solution of the alloy 
in the bottle, replacing the stopper (taking care to hold it 
in the hand whilst dropping in the solution of salt) after 
each addition, and shaking the bottle well, to clarify its con- 


PISAN IS AND FIELD’S METHODS OF ESTIMATING SILVER. 567 


tents; repeating the above routine until the last drop occa¬ 
sions no turbidity in the liquid. 

The weight of the alkalimeter and contents must now be 
again taken, and the amount of grains of salt solution em¬ 
ployed noted. 

There is most likely now in the bottle a little excess of 
salt, the amount of which must be estimated by the verify¬ 
ing solution just mentioned, in the following manner. 
Place in the other alkalimeter a certain amount (any quan¬ 
tity) of the verifying solution, and ascertain its weight with 
that of the alkalimeter, taking care to note it. Now add 
the solution, drop by drop, to the assay in the bottle, 
observing all the precautions as to agitation, &c., already 
pointed out, until the last drop causes no turbidity ; then 
weigh the alkalimeter, and note the loss of weight, and 
from the amounts of solution used calculate the standard of 
the silver alloy in thousandths. This will be rendered per¬ 
fectly clear by an example: 10 grains of alloy require for 
complete precipitation 60-7 grains of the salt solution; and 
as 10 grains of the solution are equal to 1 grain of silver, 
60 '1 is equal to 60*7 of silver ; but a slight excess of solu¬ 
tion has been added, which has increased the amount of 
silver above its true quantity ; therefore 52 grains of the 
verifying solution were added; and as each 100 grains of 
such solution contains T of a grain of silver, the 52 grains 
will contain *052 of silver, which, deducted from 6-07 = 6'018 
of silver, which gives 601 'S thousandths as the true stan¬ 
dard of the alloy operated upon. 


Mr. Sutton * has described the following modes of esti¬ 
mating silver :— 

Estimation of Silver, in Ores and Alloys, by Iodide of Starch. 
Methods of Pisani and F. Field (very accurate in the 
absence of mercury , 'protoxides, and salts of tin, iron, and 
manganese, antimony, arsenious acid, and chloride of 
gold). 

If a solution of the blue iodide of starch be added to a 
neutral solution of nitrate of silver, while any of the latter 


* Handbook of Volumetric Analysis, p. 188. London : Churchill. 



568 


THE ASSAY OF SILVER. 


is in excess the blue colour disappears, the iodine entering 
into combination with the silver ; as soon as all the silver 
is thus saturated the blue colour remains permanent and 
marks the end of the process; the reaction is veiy delicate, 
and the process accurate in the absence of the metals and 
salts mentioned above. It is more especially applicable to 
the analysis of ores and alloys of silver containing lead and 
copper. 

The solution of iodide of starch devised by Pisani, is made 
by rubbing together in a mortar 2 gm. iodine with 15 
gm. of starch and about 6 or 8 drops of water, putting the 
moist mixture into a stoppered flask and digesting in a 
water-bath for about an hour or until it has assumed a dark 
bluish-grey colour ; water is then added till all is dissolved. 
The strength of the solution is then ascertained by titrating 
it with 10 c. c. of a solution of silver containing 1 gm. in 
the litre, to which a portion of pure precipitated carbonate 
of lime is added; the addition of this latter removes all 
excess of acid, and at the same time enables the operator 
to distinguish the end of the reaction more accurately. The 
starch solution should be of such a strength that about 50 
c. c. is required for 10 c. c. of the silver solution ( = 0’01 gm. 
silver). 

F. Field,* who discovered the principle of this method 
simultaneously with Pisani, uses a solution of iodine in 
iodide of potassium with starch liquor. Those who desire 
to make use of this plan can use deci- and centi-normal 
solutions of iodine, the results being the same in either case. 

In the analysis of silver containing copper the solution 
must be considerably diluted in order to weaken the colour 
of the copper, a small measured portion is then taken, car¬ 
bonate of lime added, and iodide of starch till the colour is 
permanent. It is best to operate with about from 60 to 100 
c. c., containing not more than 0-02 gm. silver ; when the 
quantity is much greater than this it is preferable to preci¬ 
pitate the greater portion with chloride of sodium, and 
to complete with iodide of starch after filtering off the chlo¬ 
ride. When lead is present with silver in the nitric acid 

* Chem. News, vol. ii. p. 17. 


GAY-LUSSAC S METHOD MODIFIED BY J. G. MULDER. 569 

solution, add sulphuric acid and filter off the sulphate of 
lead, then add carbonate of lime to neutralise excess of acid, 
filter again, if necessary, then add fresh carbonate of lime 
and titrate as above. 


Assay of Commercial Silver (Plate, Bullion , Coin , $c.). 
Gay-Lussac’s Method modified by J. G. Mulder. 


For more than thirty years Gay-Lussac’s method of esti¬ 
mating silver in its alloys has been practised intact, at all the 
European mints, under the name of the 4 humid method,’ in 
place of the whole system of cupellation; during that time 
it has been regarded as one of the most exact methods of 
quantitative analysis; the researches of Mulder, however, 
into the innermost details of the process liave shown that it 
is capable of even greater accuracy than has hitherto been 
gained by it. For the particulars of Mulder’s investigations 
I cannot do better than refer the reader to the excellent 
translation of his memoir, published in the ‘ Chemical News,’ 
by Dr. Adriani. 

The principle of the process is the affinity which chlorine 
has for silver in preference to all other substances, and 
resulting in the formation of chloride of silver, a compound 
insoluble in dilute acids, and which readily separates itself 
from the liquid in which it is suspended. 

The plan originally devised by the illustrious inventor of 
this process for assaying silver, and which is still followed, is 
to consider the weight of alloy taken for examination to 
consist of 1000 parts, and the question is to find how many 
of these parts are pure silver. This empirical system was 
arranged for the convenience of commerce, and being now 
thoroughly established it is the best plan of procedure ; if, 
therefore, standard solution of salt be made of such strength 
that 100 c. c. will exactly precipitate 1 gramme of silver, it 
is manifest that eacli T *y c. c. will precipitate 1 milligramme 
or yy^yth part of the gramme taken, and consequently in 
the analysis of l gramme of any alloy containing silver, the 
number of yL 0 - c. c. required to precipitate all the silver out 


570 


TI1E ASSAY OF SILVER. 


« 


of it would be the number of thousandths of pure silver 
contained in the specimen. 

In practice, however, it would not do to follow this plan 
precisely, inasmuch as neither the measurement of the stan¬ 
dard solution nor the ending of the process would be gained 
in the most exact manner, consequently a decimal solution 
of salt, one-tenth the strength of the standard solution, is 
prepared, so that 1000 c. c. will exactly precipitate 1 gramme 
of silver, and, therefore, 1 c. c. one milligramme. 

The silver alloy to be examined (the composition of 
which must be approximately known) is weighed so that 
about 1 gramme of pure silver is present; it is then dissolved 
in pure nitric acid by the aid of a gentle heat, and 100 c. c. 
of standard solution of salt added from a pipette in order to 
precipitate exactly 1 gm. of silver, the bottle containing the 
mixture is then well shaken until the chloride of silver has 
curdled, leaving the liquid clear. 

The question is now—Which is in excess, salt or silver ? 
A drop of decimal salt solution is added, and if a pre¬ 
cipitate is produced, 1 c. c. is delivered in, and after 
clearing, another, and so on, as long as a precipitate is pro¬ 
duced ; if, on the other hand, the one drop of salt produced 
no precipitate, showing that the pure silver present was less 
than 1 gm., a decimal solution of silver is used, prepared 
by dissolving 1 gm. pure silver in pure nitric acid and 
diluting to 1 litre ; this solution is added after the same 
manner as the salt solution just described, until no further 
precipitate occurs; in either case the quantity of decimal 
solution used is noted, and the results calculated in thou¬ 
sandths for 1 gm. of the alloy. 

The process thus shortly described is that originally de¬ 
vised by Gay-Lussac, and it was taken for granted that when 
equivalent chemical proportions of silver and chloride of 
sodium were brought thus in contact that every trace of the 
metal was precipitated from the solution, leaving nitrate of 
soda and free nitric acid only in solution. The researches 
of Mulder, however, go to prove that this is not strictly the 
case, but that when the most exact chemical proportions of 
silver and salt are made to react on each other, and the 


GAY-LUSSAC’S METHOD MODIFIED BY J. G. MULDER. 


571 


chloride lias subsided, a few drops more of either salt or 
silver solution will produce a further precipitate, indicating 
the presence of both nitrate of silver and chloride of sodium 
in a state of equilibrium, which is upset on the addition of 
either salt or silver. Mulder decides, and no doubt rightly, 
that this peculiarity is owing to the presence of nitrate of 
soda, and varies somewhat with the temperature and state 
of dilution of the liquid. 

It therefore follows that when a silver solution is carefully 
precipitated, first by concentrated and then by dilute salt 
solution, until no further precipitate appears, the clear 
liquid will at this point give a precipitate with dilute silver 
solution, and if this be added till no further cloudiness is pro¬ 
duced, it will again be precipitable by dilute salt solution. 

For example: suppose that in a given silver analysis the 
decimal salt solution has been added so long as a precipitate 
is produced, and that 1 c. c. (= 20 drops of Mulder’s dropping 
apparatus) of decimal silver is in turn required to precipitate 
the apparent excess, it would be found that when this had 
been done, 1 c. c. more of salt solution would be wanted to 
reach the point at which no further cloudiness is produced 
by it, and so the changes might be rung time after time; if, 
however, instead of the last 1 c. c. (= 20 drops) of salt, half 
the quantity be added, that is to say 10 drops ( = 1 c. c.); 
Mulder’s so-called neutral point is reached, namely, that in 
which, if the liquid be divided in half, both salt and silver 
will produce the same amount of precipitate. At this stage 
the solution contains chloride of silver dissolved in nitrate 
of soda, and the addition of either salt or silver expels it 
from solution. 

A silver analysis may therefore be concluded in three 
ways— 

1. By adding decimal salt solution until it just ceases to 
produce a cloudiness. 

2. By adding a slight excess of salt, and then decimal 
silver till no more precipitate occurs. 

3. By finding the neutral point. 

According to Mulder, the latter is the only correct method, 
and preserves its accuracy at all temperatures up to 56° C. 


572 


THE ASSAY OF SILVER. 


(= 133° Fahr.), while tlie difference between 1 and 3 amounts 
to i a milligramme, and that between 1 and 2 to 1 milli¬ 
gramme on 1 gramme of silver at 10° C. ( = 62° Fahr.), and 
is seriously increased by variation of temperature. 

It will readily be seen that much more trouble and care 
is required by Mulder’s method than by that of Gay-Lussac, 
but as a compensation, much greater accuracy is obtained. 

On the whole, it appears to me preferable to weigh the 
alloy so that slightly more than 1 gm. of silver is present, 
and to choose the ending No. 1, adding drop by drop the 
decimal salt solution until just a trace of precipitate is seen, 
and which, after some practice, is known by the operator to 
be final. It will be found that the quantity of salt solution 
used will slightly exceed that required by chemical com¬ 
putation—say 100’1 c.c. are found equal to 1 gm. silver, 
the operator has only to calculate that quantity of the salt 
solution in question for every 1 gm. silver he assays in the 
form of alloy, and the error produced by the solubility of 
chloride of silver in nitrate of soda is removed. 

If the decimal solution has been cautiously added, and 
the temperature not higher than 62° Fahr., this method of 
conclusion is as reliable as No. 3, and free from the possible 
errors of experiment, for it requires a great expenditure 
of time and patience to reverse an assay two or three times, 
and each time cautiously adding the solutions, drop by drop, 
then shaking and waiting for the . liquid to clear, beside 
the risk of discolouring the chloride of silver, which would 
at once vitiate the results. 

The decimal silver solution, according to this arrange¬ 
ment, would seldom be required ; if the salt has been in¬ 
cautiously added, or the quantity of alloy too little to 
contain 1 gm. pure silver, then it is best to add once for all 
2, 3, or 5 c.c. according to circumstances, and finish with 
decimal salt as No. 1, deducting the silver added. 

The Standard Solutions and Necessary Apparatus. 

a. Standard Solution of Salt.— Pure chloride of sodium is 
prepared by treating a concentrated solution of the whitest 


GAY-LUSSAC’S METHOD MODIFIED BY J. G. MULDER. 


573 


table salt first with a solution of caustic baryta to remove 
sulphuric acid and magnesia, then with a slight excess of 
carbonate of soda to remove baryta and lime, warming and 
allowing the precipitates to subside ; then evaporating to a 
small bulk, that crystals may form; these are separated by a 
filter, and slightly washed with cold distilled water ; dried,re- 
- moved from the filter, and heated to a dull redness, and when 
cold preserved in a well-closed bottle for use. The mother 
liquor is thrown away or used for other purposes. Of the 
salt so prepared, or of chemically pure rock-salt (steinsalz, a 
substance to be obtained freely in Germany) 5*4145 gm. is to 
be weighed and dissolved in 1 litre of distilled water at 
62° Fahr. 100 c. c. of this solution will precipitate exactly 
1 gm. silver ; it is preserved in a well-stoppered bottle, and 
shaken before use. 

j Decimal Solution of Salt .—100 c. c. of the above solution 
is diluted to exactly 1 litre with distilled water at 62° Fahr. 
1 c. c. will precipitate 0 001 gm. silver. 

b. Decimal Solution of Silver .—Pure metallic silver is 
best prepared by galvanic action from pure chloride ; and 
as clean and secure a method as any, is to wrap a lump of 
clean zinc, into which a silver wire is melted, with a piece 
of wetted bladder or calico, so as to keep any particles of 
impurity contained in the zinc from the silver. The chloride 
is placed at the bottom of a porcelain dish, covered with 
dilute sulphuric acid, and the zinc laid in the middle ; the 
silver wire is bent over so as to be immersed in the chloride ; 
as soon as the acid begins to act upon the zinc, the reduction 
commences in the chloride and grows gradually all over the 
mass ; the resulting finely-divided silver is well washed, 
first with dilute acid, then with hot water, till all acid and 
soluble zinc are removed. 

The moist metal is then mixed with a little carbonate of 
soda, saltpetre, and borax, say about an eighth part of each, 
and dried perfectly. 

The metallic silver obtained as above is never free 
altogether from organic matter and undecomposed chloride, 
and, therefore, it must invariably be melted. Mulder re¬ 
commends that the melting should be done in a porcelain 



574 


THE ASSAY OF SILVER. 


crucible, immersed in sand contained in a common earthen 
crucible ; borax is sprinkled over the surface of the sand so 
that it may be somewhat vitrified, that in pouring out the 
silver when melted no particles of dirt or sand may fall into 
it. If the quantity of metal is small it may be melted in a 
porcelain crucible over a gas blowpipe. 

The molten metal obtained in either case can be poured 
into cold water and so granulated, or upon a slab of pipe¬ 
clay, into which a glass plate has been pressed when soft so 
as to form a shallow mould. The metal is then washed well 
with boiling water to remove accidental surface impurities, 
and rolled into thin strips by a goldsmith’s mill, in order 
that it may be readily cut for weighing; the granulated metal 
is, of course, ready for use at once without any rolling. 

1 gm. of this silver is dissolved in pure dilute nitric acid 
and diluted to 1 litre—each c.c. contains 0*001 gm. silver— 
it should be kept from the light. 

Dropping Apparatus for concluding the Assay. —Mulder 
constructs a special affair for this purpose, consisting of a 
pear-shaped vessel fixed in a stand, with special arrange¬ 
ments for preventing any continued flow of liquid ; the 
delivery* tube has an opening of such size that 20 drops 
measure exactly 1 c. c.—the vessel itself is not graduated. As 
this arrangement is of more service to assay than to general 
laboratories, it need not be further described here. A small 
burette divided in c. c. with a convenient dropping tube 
will answer every purpose, and possesses the further advan¬ 
tage of recording the actual volume of fluid delivered. 

The 100 c.c. pipette, for delivering the concentrated salt 
solution, must be accurately graduated, and should deliver 
exactly 100 gm. of distilled water at 62° Fahr. 

The test bottles, holding about 200 c. c. should have their 
stoppers well ground and brought to a point, and should be 
fitted into japanned tin tubes reaching as high as the neck, 
so as to preserve the precipitated chloride from the action of 
light, and, when shaken, a piece of black cloth should be 
covered over the stopper. 

c. Titration of the Standard Salt Solution .—It is not 
possible to rely absolutely upon a standard solution of salt, 




GAY-LUSSAC’S METHOD MODIFIED BY J. G. MULDER. 575 

containing 5-4145 gm. per litre, although this is chemically 
correct in its strength. The real working power must be 
found by experiment. From 1*002 to 1*004 gm. of abso¬ 
lutely pure silver is weighed on the assay balance, put into 
a test bottle with about 5 c. c. of pure nitric acid about 1*2 
spec, grav., and gently heated in the water or sand bath till 
it is all dissolved. The nitrous vapours are then blown 
from the bottle, and it is set aside to cool down to about 
62° Fahr. 

The 100 c. c. pipette, which should be securely fixed in a 
support, is then carefully filled with the salt solution, and 
delivered into the test bottle contained in its case, the 
moistened stopper inserted, covered over with the black 
velvet or cloth, and shaken continuously till the chloride 
has clotted and the liquid becomes clear; the stopper is 
then slightly lifted and its point touched against the neck of 
the bottle to remove excess of liquid, again inserted, and any 
particles of chloride washed down from the top of the 
bottle by carefully shaking the clear liquid over them. The 
bottle is then brought under the decimal salt burette, and ^ c. c. 
added, the mixture shaken, cleared, another \ c. c. put in, and 
the bottle lifted partly out of its case to see if the precipitate 
is considerable ; lastly, 2 or 3 drops only of the solution are 
added at a time until no further opacity is produced by the 
final drop. Suppose, for instance, that in titrating the salt 
solution it is found that 1-003 gm. silver require 100 c. c. 
concentrated, and 4 c. c. decimal solution, altogether equal 
to 100*4 c. c. concentrated, then— 

1-003 silver : 100*4 salt:: 1-000 : ^=100*0999. 

The result is within T o,Wo °f 100*1? which is near enough 
for the purpose and may be more conveniently used. The 
operator, therefore, knows that 100*1 c. c. of the concentrated 
salt solution at 62° Fahr. will exactly precipitate 1 gm. silver, 
and calculates accordingly in his examination of alloys. 

In the assay of coin and plate of the English standard, 
namely, 11*1 silver and 0*9 copper, the weight corresponding 
to 1 gm. silver is 1*081 gm., therefore, in examining this 
alloy 1*085 gm. may be weighed. 


57G 


THE ASSAY OF SILVER. 


When the quantity of silver is not approximately known, 
a preliminary analysis is necessary, which is best made by 
dissolving J- or 1 gm. of the alloy in nitric acid, and pre¬ 
cipitating very carefully with the concentrated salt solution 
from a c. c. burette. Suppose that in this manner 1 gm. 
of alloy required 45 c. c. salt solution, 

100T salt : 1-000 silver 45 : # = 0*4495, arid again 
0 4495 : 1 :: 1-003 : a=2-231. 

2*231 gm. of this particular alloy are therefore taken for 
the assay. 

Where alloys of silver contain sulphur or gold, with small 
quantities of tin, lead, or antimony, they are first treated 
with a small quantity of nitric acid so long as red vapours 
are disengaged, then boiled with concentrated sulphuric 
acid till the gold has become compact, set aside to cool, 
diluted with water, and titrated as above. 

BLOWPIPE REACTIONS OF SILVER. 

ORES OF SILVER. 

Sulphide of Silver.— Alone, on charcoal, fuses and swells 
considerably, forming large bubbles ; but after a continued 
blast, it forms a grain. It gives off an odour of sulphurous 
acid, and finally furnishes a grain of silver, surrounded by 
slag. Fused with borax and microcosmic salt, the slag gives 
traces of copper. 

Red Silver.— Alone , on charcoal, decrepitates little, fuses, 
burns and smokes, like antimony, but gives no arsenical 
odour. The production of vapour lasts but for a few 
minutes. 

In the open tube , it gives much vapour, and a smell of 
sulphurous acid, which is very strong at the commencement. 
The deposit on the sides of the tube is sometimes crystal¬ 
line ; it is oxide of antimony. The bead which remains 
after a long exposure to the exterior flame is a button 
of pure silver. 

Antimonial Silver, and Argentiferous Antimony. — Alone , 
on charcoal, fuses readily, forming a metallic bead, which is 



BLOWPIPE REACTIONS OP SILVER. 


577 


not malleable, giving off a vapour like that of pure antimony, 
but less abundant. The bead becomes, after the dis¬ 
engagement of a certain quantity of antimony, dull white, 
and very crystalline, entering into ignition at the instant of 
congelation. When it has lost still more antimony, its 
surface becomes smooth, like glass ; and the heat which it 
then disengages is more intense than at any other time. 
Lastly, after a long-continued blast, nothing but pure silver 
remains. 

In the tube, much oxide of antimony is given off, and the 
bead which remains is surrounded by a bead of deep yellow 
glass. 

Electrum gives by fusion a grain of gold, which varies in 
whiteness, and which gives with borax and microcosmic salt 
the same reactions as pure silver. 

Amalgam, in the matrass, swells up, and gives much 
mercury, leaving silver, which may be fused to a bead on 
charcoal. 

Chloride of Silver, Horn Silver. —On charcoal becomes a 
bead, which, according to the purity of the salt, is grey, 
brownish, or black. In the reducing flame it is gradually 
converted into metallic silver. It gives with microcosmic 
salt, fused on the platinum wire, a blue flame, like the 
chloride of mercury. 

Oxide of Silver. — Alone , is reduced instantaneously. 

With borax a part is dissolved and a part reduced. In 
the oxidising flame the glass becomes, on cooling, milk- 
white, taking the colours of the opal, according to the 
quantity of the silver dissolved. In the reducing flame it 
becomes greyish, owing to the dissemination of particles of 
metallic silver. 

With microcosmic salt the oxide and the metal give 
in the oxidising flame a yellowish opaline glass; seen 
by refraction, in the day it appears yellow; seen in the 
same manner by the light of the lamp it appears reddish. 

This is the most appropriate place to introduce the 
valuable and highly interesting researches on the applica¬ 
tion of the blowpipe to the assay of silver, by David 


578 


TI1E ASSAY OF SILVER. 


Forbes, F.R.S., as given in the Chemical News , Nos. 380, 
384, 392, 396, 398, and 412. 

The blowpipe assay of silver ores was first described 
in 1827 by Harkort,* and subsequently considerably 
improved by Plattner. This assay process is in all cases 
based upon the reduction to a metallic state of all the 
silver contained in the compound in question along with 
more or less metallic lead, which latter metal, when 
not already present in sufficient quantity in the substance 
itself under examination, is added in the state of granulated 
lead to the assay previous to its reduction. The globule 
of silver-lead thus obtained, if soft and free from such 
elements as would interfere with its treatment upon the 
cupel, may then be at once cupelled before the blowpipe 
until the pure silver alone remains upon the bone ash 
surface of the cupel ; but if not, it is previously submitted 
to a scorifying or oxidating treatment upon charcoal until 
all such substances are either slagged off or volatilised, 
and the resulting silver-lead globule cupelled as before. 

As, therefore, the final operation in all silver assays 
is invariably that of cupelling the silver-lead alloy obtained 
from the previous reduction of the substance, effected by 
methods differing according to the nature of the argen¬ 
tiferous ore or compound under examination, it is here 
considered advisable to introduce the description of the 
silver assay by an explanation of this process. 

In the ordinary process of cupellation in the muffle, bone- 
ash or other cupels are employed of a size large enough to 
absorb the whole of the litharge produced from the oxida¬ 
tion of the lead in the assay. 

This, however, should not be the case when using the 
blowpipe ; for as the heating powers of that instrument are 
limited, it is found in practice much better to accomplish 
this result by two distinct operations—the first being a 
concentration of the silver-lead in which the greater part 
of the lead is converted by oxidation into litharge re¬ 
maining upon, but not, or only very slightly, absorbed by, 
the bone-ash cupel; and the second in cupelling the small 

* Die Probirkunst mit clem Lothrohre. Freiberg, 1827, I. Heft (all published). 


FORBES'S BLOWPIPE ASSAY. 


579 


concentrated metallic bead so obtained upon a fresh cupel 
until the remaining lead is totally absorbed by the cupel 
and the silver left behind in a pure state. By this means a 
much larger weight of the silver-lead alloy can be sub¬ 
mitted to assay, and, for reasons hereafter to be explained, 
much more exact results are obtained than would be the 
case when the cupellation is conducted at one operation 
in the ordinary manner. 

The apparatus used by the author for these operations 
are shown to a scale ot one-half their real size in the 
woodcuts fig. 126 (a to d). 

In fig. 126 a represents in section a small cylindrical 
mould of iron, seven-tenths of an inch in diameter, and about 
four-tenths high, in which is turned a 
cup-shaped nearly hemispherical depres¬ 
sion two-tenths of an inch deep in 
centre, the inner surface of which is left 
rough, or marked with minute ridges 
and furrows for the purpose of enabling 
it to retain more firmly the bone-ash 
lining which is stamped into it by means 
of the polished bolt, also shown in the 
figure. This mould rests upon the stand 
cl , having for this purpose a small cen¬ 
tral socket in its base, into which the 
central pivot of the stand enters. This 
socket is seen in the ground plan b of 
the base of the mould, which shows likewise three small 
grooves or slots made to enable a steady hold to be taken 
of it, when hot, by the forceps. The stand itself is com¬ 
posed of a small turned ivory or wood base, fixed into a 
short piece of strong glass tubing, which, from its non¬ 
conducting powers, serves as an excellent handle. In the 
centre of the base a slight iron rod rising above the level 
of the glass outer tube serves as a support for the cupel 
mould, into the socket in the base of which it enters. 

Bone ash is best prepared by burning bones which pre¬ 
viously had been boiled several times, so as to extract all 
animal matter. The best bone ash is made from the eore- 


Fig. 126. 













580 


TIIE ASSAY OF SILVER. 


bone of the horns of cattle well boiled out and burned. 
The ash from this is more uniform than from the other 
bones, which have in general a very compact enamel-like 
exterior surface, whilst the interior is of a much softer 
nature. 

Concentration of the Silver-lead .—A cupel is prepared 
by filling the above described cupel mould with bone-ash 
powder not finer than will pass through a sieve containing 
from forty to fifty holes in the linear inch, and should be 
well dried and kept in an airtight bottle, and the whole 
pressed down with the bolt, using a few taps of the hammer. 
It is then heated strongly in the oxidating blowpipe flame, 
in order to drive off any hygroscopic moisture. The bone- 
ash surface of the cupel, after heating, should be smooth, 
and present no cracks ; if the reverse, these may be re¬ 
moved by using the bolt again and reheating.* The silver- 
lead, beaten on the anvil into the form of a cube, is placed 
gently upon the surface of the bone ash, and, directing a 
pretty strong oxidating flame on to its surface, it is fused, 
and quickly attains a bright metallic appearance, and 
commences to oxidise with a rapid rotatory movement. 
(Occasionally, when the assay is large, and much copper or 
nickel present, the globule may, under this operation, cover 
itself with a crust of oxide of lead or solidify ; in such 
cases direct the blue point of a strong flame steadily on 
to one spot on the surface of the lead globule until it 
commences oxidating and rotating. In some cases where 
much nickel is present, an infusible scale, impeding or even 
preventing this action, may form, but will disappear on 
adding more lead—say from three to six grains, according 
to the thickness of this scale or crust.) When this occurs, 
the cupel is slightly inclined from the lamp, and a fine blue 
point obtained by placing the blowpipe nozzle deeper into 
the flame, and the lamp is directed at about an angle of 30° 
on to the globule—not, however, so near as to touch it 
with the blue point, but only with the outer flame, so 

* These precautions are very important, as the slightest trace of moisture in 
the substance of the bone ash would inevitably cause a spirting of the metal 
during the operation. 




forbes’s blowpipe assay. 


5S1 


moderating it as to keep the assay at a gentle red heat, and 
not allowing the rotation to become too violent. 

This oxidating fusion should be carried on at the lowest 
temperature sufficient to keep up the rotatory movement, 
and to prevent a crust of litharge accumulating upon the 
surface of the globule, but still sufficiently high to hinder 
the metallic globule from solidifying. Should this, how¬ 
ever, happen, a stronger flame must be employed for a 
moment until the metal is again in rotation ; such interrup¬ 
tions should, however, be avoided. The proper temperature 
can only be learned by practice; a too high temperature 
is still more injurious, causing the lead to volatilise, and, if 
rich in silver, carry some of that metal mechanically along 
with it. The litharge also, instead of remaining on the 
cupel, would be absorbed by the bone ash, and as the 
surface of the metallic globule is covered by a too thin 
coating of fused litharge, some silver may be absorbed 
along with the litharge. In this operation, in order to 
avoid loss of silver, the fused globule should be always 
kept in contact with the melted litharge. 

By the above treatment, the air has free access to the 
assay, and the oxidation of the lead and associated foreign 
metals goes on rapidly. The surface of the melted globule, 
when poor in silver, shows a brilliant play of iridescent 
colours, which does not take place when very rich in silver. 
The litharge is driven to the edge of the globule, heaping 
itself up and solidifying behind and around it. When the 
globule becomes so hemmed in by the litharge as to present 
too small a surface for oxidation, the cupel is moved so as 
to be more horizontal (having been previously kept on an 
inclined position), thus causing the lead globule to slide by 
its own weight on one side, and expose a fresh surface 
to the oxidising action. When the lead is pure, the litharge 
formed has a reddish-yellow colour, but, if copper is present, 
is nearly black. 

In concentrating silver-lead, it must be remembered that 
an alloy of lead and silver, if in the proportion of about 86 
per cent, silver along with 14 per cent, lead, when cooled 
slowly in the litharge behaves in a manner analogous to 


582 


THE ASSAY OF SILVER. 


the spitting of pure silver, throwing out a whitish-grey 
pulverulent excrescence rich in silver. For this reason, 
therefore, the concentration above described should be 
stopped when the globule is supposed to contain about six 
parts silver along with one part in weight of lead. In case, 
however, this limit should have been exceeded, it is advisable 
at once to push the concentration still further until the 
silver globule contains but very little lead. In practice 
with poor ores it is usual to concentrate the lead until 
the globule is reduced to the size of a small mustard seed, 
or in rich ores to some two or three times that size. Upon 
arriving at this point, the cupel is withdrawn very gradually 
from the flame, so that the cooling shall take place as slowly 
as possible until the globule has solidified in its envelope of 
litharge. If cooled too quickly, the litharge, contracting 
suddenly, would throw out the globule, or even cause it 
to spirt; in such case it should be touched by the point of 
the blue flame so as to fuse it to a round globule, which is 
cooled slowly, as before described. The globule is now 
reserved for the next operation, for which purpose it is, 
when quite cold, extracted from the litharge surrounding it. 

Cupellation .—The bone ash required for this process 
should be of the best quality and in the most impalpable 
powder, prepared by elutriating finely-ground bone ash, 
and drying the product before use. 

The cupel, still hot from the last operation, is placed upon 
the anvil, and the crust of litharge, with its enclosed me¬ 
tallic bead, gently removed, leaving the hot coarse bone ash 
beneath it in the mould ; upon this a small quantity of the 
elutriated bone ash is placed, so as to fill up the cavity, and 
the whole, whilst hot, stamped down by the bolt, previously 
slightly warmed, with a few taps of the hammer. The 
cupel thus formed is heated strongly in the oxidating flame, 
which should leave the surface perfectly smooth, and free 
from any fissures or scales; if such appear, the bolt must 
again be used, and the cupel re-heated. In this process it 
is very important that the cupel should possess as smooth a 
surface as possible, whilst at the same time the substance 
of the cupel beneath should not be too compact, so as 



forbes’s blowpipe assay. 


583 


thereby to permit the litharge to filter through and be 
readily absorbed, leaving the silver bead upon the smooth 
upper surface. 

The bead of silver-lead obtained from the last operation 
is taken out of the litharge in which it is embedded, and, 
alter removing any trace of adherent bone ash or litharge, 
is slightly flattened to prevent its rolling about upon the 
surface of the cupel. 

It is now put into the cupel prepared as before described, 
placing it on the side furthest from the lamp and a little 
above the centre of the cupel, which is now inclined 
slightly towards the lamp, and is heated by the oxidating 
flame directed downwards upon it, this causing the globule, 
when fused and oxidating, to move of itself into the centre 
of the cupel. The cupel is now brought into a horizontal 
position, and the flame, directed on to it at an angle of about 
forty-five degrees, is made to play upon the bone-ash surface 
immediately surrounding the globule, without, however, 
touching it, so as to keep this part of the cupel at a red 
heat sufficiently strong to insure the globule being in con¬ 
stant oxidising fusion, at the same time to cause the perfect 
absorption of the litharge, so as to prevent any scales of 
litharge forming upon the surface of the cupel under the 
globule, which would impede the oxidation, as well as pre¬ 
vent the silver bead being easily detached at the conclusion 
of the operation. Should the heat at any time be too low 
and the globule solidify, it must be touched for an instant 
with the point of the flame and proceeded with as before. 
Should (in consequence of the bone ash not having been 
sufficiently heated to absorb the litharge perfectly) a little 
litharge adhere pertinaciously to the globule, or a particle 
of the bone-ash cupel attach itself, the cupel should be 
slightly inclined, so as to allow the globule to move by its 
own weight on to another and clean part of the cupel, 
leaving the litharge or bone ash behind it; but, if not suffi¬ 
ciently heavy to do so, a small piece of pure lead may be 
fused to it in order to increase its weight, and so allow of 
the same proceeding being adopted. 

By slightly inclining the cupel stand, and moving it so as 


584 


THE ASSAY OF SILVER. 


to present in turn all parts of the surface surrounding the 
globule to the action of the flame, the cupellation proceeds 
rapidly. If, however, the assay contains very little silver, 
it will be found necessary to move the globule from one 
spot to another on the cupel, in order to present a fresh 
surface for absorbing the litharge formed; this is done by 
simply inclining the cupel stand, remembering that the 
bone ash surrounding the globule must always be kept at 
a red heat, without ever touching the globule itself by the 
flame. 

In assays rich in silver a play of iridescent colours ap¬ 
pears some seconds before the 4 brightening,’ which dis¬ 
appears the moment the silver becomes pure ; as soon as 
this is observed the cupel should be moved in a circular 
manner, so that the globule is nearly touched all round by 
the point of the blue flame, and this is continued until the 
surface of the melted silver is seen to be quite free from any 
litharge, upon which it is very gradually withdrawn from 
the flame so as to cool the assay by degrees very slowly, in 
order to prevent 4 spitting . 5 

When the silver-lead is very poor, this play of colours is 
not apparent, and as soon as the rotatory movement of the 
globule ceases, the heat must be increased for an instant, in 
order to remove the last thin but pertinacious film or sca^ 
of litharge, and subsequently the assay is cooled gradually; 
when cold it should, whilst still upon the cupel, be examined 
by a lens, to see whether the bead possesses a pure silver 
colour, as, if not, it must be re-heated. 

Frequently, when the ‘brightening’ takes place, the 
silver globule is found to spread out, and, after cooling, 
although of a white colour, is found to appear somewhat 
less spherical or more flattened in shape than a correspond¬ 
ing globule of pure silver would be. This arises from the 
presence of copper still remaining in the silver, and in such 
cases a small piece of pure lead (about from one-half to one 
and a half grain in weight, according to size of assay) should 
be fused on the cupel along with the silver, and the cupel¬ 
lation of the whole conducted as before on another part of 
the cupel, when the silver globule will be obtained pure, 



forbes’s blowpipe assay. 


585 


and nearly spherical in shape. Sometimes the silver globule 
in 4 brightening ’ may still remain covered with a thin film 
of litharge, although otherwise pure ; this arises from too 
little heat having been employed in the last stage of the 
operation, and consequently the bead should be re-heated 
iu a strong oxidating flame until this litharge is absorbed, 
and the globule, after slow cooling, appears pure. 

If the instructions here given be strictly attended to, it 
will be found after some practice, that very accurate results 
may be obtained in the blowpipe assay for silver, and that 
no difficulty will be found in detecting the presence and 
determining the amount of silver present, even when in as 
small a quantity as half an ounce to the ton. When sub¬ 
stances containing very little silver or less than that amount 
are examined, several assays should be made, and the 
silver-lead obtained concentrated separately, after which 
the various globules should be united and cupelled together 
in one operation. 

It is hardly necessary to remark, that the lead employed 
in assaying should be free from silver, or if not, its actual 
contents in silver should be determined, and subtracted from 
the amount found in the assay. 

Assay lead containing less than one quarter of an ounce 
to the ton of lead can readily be obtained, or can be made 
by precipitating a solution of acetate of lead by metallic 
zinc, rejecting the first portion of lead thrown down. In 
all cases the lead should be fused and granulated finely— 
the granulated lead for use in these assays being previously 
passed through a sieve containing forty holes to the linear 
inch. It is also useful to have some lead in the form of 
wire, as being being very convenient for adding in small 
portions to assays when on the cupel. 

Determination of the Weight of the Silver Globule obtained 
on Cupellation .—As the amount of lead which can, by the 
method before described, be conveniently cupelled before 
the blowpipe, is necessarily limited, the silver globule which 
remains upon the bone-ash surface of the cupel at the end 
of the operation is, when substances poor in silver have 
been examined, frequently so very minute that its weight 



586 


THE ASSAY OF SILVER. 


could not be determined with correctness by the most deli¬ 
cate balances in general use. 

The blowpipe balance employed by the author turns 
Fig. 127. readily with one-thousandth of a grain, but 
could not be used for determining weights 
below that amount. 

Globules of silver of far less weight than 
one-thousandth are distinctly visible to the 
naked eye—a circumstance which induced 
Harkort to invent a volumetrical scale based 
upon the measurement of the diameters of the 
globules, which scale in practice has been found 
of very great utility in the blowpipe assay of 
silver. 

The scale for this purpose which is employed 
by the author is shown in full size in the an¬ 
nexed woodcut. 

This figure represents a small strip of highly 
polished ivory about inches long, J- inch 
broad, and ^ inch in thickness, on which are 
drawn, by an extremely line point, two very 
fine and distinct lines emanating from the 
lower or zero point, and diverging upwards 
until, at the distance of exactly six English 
standard inches, they are precisely four-hun¬ 
dredth parts of an inch apart. This distance 
(six inches) is, as shown in woodcut, divided 
into 100 equal parts by cross lines numbered 
in accordance from zero upwards. It is now 
evident, if a small globule of silver be placed 
in the space between these two lines, using a 
magnifying glass to assist the eye in moving it 
up or down until the diameter of the globule is 
exactly contained within the lines themselves, 
that we have at once a means of estimating 
the diameter of the globule itself, and therefrom 
are enabled to calculate its weight. 

As the silver globules which cool upon the 
surface of the bone-ash cupel are not true 

























































forbes’s blowpipe assay. 


587 


spheres, but are considerably flattened on the lower surface, 
where they touch and rest upon the cupel, it follows that 
the weight of globules corresponding in diameter to the 
extent of divergence at the different degrees of the scale can¬ 
not be calculated directly from their diameters as spheres, 
but require to have their actual weight experimentally 
determined in the same manner as employed by Plattner. 

The table here appended has been calculated by the 
author, and in one column shows the diameter in English 

o 

inches corresponding to each number or degree of the scale 
itself, and in the two next columns the respective weights of 
the flattened spheres which correspond to each degree or 
diameter; for convenience these weights are given in the 
different columns in decimals, both of English grains and of 
Erench grammes. 

These weights are calculated from the following data, 
found as the average result of several very careful and 
closely approximating assays, which showed that globules of 
silver exactly corresponding to No. 95 on this scale, or 0-038 
inch in diameter, possessed a weight of 0-0475573 grains or 
0-003079 grammes. From this the respective weights of 
all the other numbers or degrees on this scale were calcu¬ 
lated, on the principle that solids were to one another in 
the ratio of the cubes of their diameters. This mode of 
calculation is not, however, absolutely correct in principle, 
for the amount of flattening of the under surface of the 
globule diminishes in reality with the decreasing volume of 
the globule. In actual practice, however, this difference 
may be assumed to be so small that it may be neglected 
without injury to the correctness of the results. 

The smaller the diameter of the globule, the less will be 
the difference or variation in weight in descending the 
degrees of this scale, since the globules themselves vary in 
weight with the cubes of their diameters ; for this reason, 
also, all such globules as come within the scope of the 
balance employed should be weighed in preference to being 
measured, and this scale should be regarded as more spe¬ 
cially applicable to the smaller globules beyond the reach 
of the balance. 


588 


THE ASSAY OF SILVER. 


No. on 
scale 

Greatest diameter 
in inches 

Weight of globule in 
grains 

Weight of globule in 
grammes 

1 

00004 

0 00000005 

0-000000003 

2 

00008 

0-00000044 

0-000000028 

3 

00012 

0-00000149 

0-000000096 

4 

00016 

0-00000355 

0-000000229 

5 

0-0020 

0-0000069 

0-00000044 

G 

00024 

0-0000119 

000000077 

7 

0 0028 

00000190 

0-00000120 

8 

00032 

0-0000284 

0 00000184 

9 

00036 

0-0000403 

0-00000262 

10 

00040 

00000554 

0-00000359 

11 

00044 

0 0000736 

0-00000478 

12 

0 0048 

0 0000958 

0 00000620 

13 

0-0052 

0-0001218 

0-00000789 

14 

0-0056 

0-0001522 

0 00000985 

15 

0-0060 

0-0001872 

0 00001203 

16 

00064 

0-0002272 

0 00001471 

17 

0-0068 

0 0002725 

0-00001764 

18 

0-0072 

0-0003234 

0-00002094 

19 

00076 

0-0003804 

0 00002463 

20 

0-0080 

00004437 

0-00002872 

21 

0-0084 

00005137 

0 00003327 

22 

0-0088 

0-0005906 

0-00003823 

26 

0 0092 

00006748 

0-00004367 

24 

00096 

0-0007668 

0-00004964 

25 

o-oioo 

0-0008667 

0-00005611 

26 

00104 

0-0009749 

0-00006311 

27 

0-0108 

00010918 

0-00007068 

28 

0-0112 

00012176 

0-00007883 

29 

00116 

00013528 

0-00008758 

30 

0-0120 

0-0014976 

0-00009696 

31 

00124 

0-0016524 

0-00010698 

32 

00128 

0-0018176 

0-00011677 

33 

00132 

0 0019934 - 

0-00012817 

34 

0-0136 

0-0021801 

000014114 

35 

0-0140 

0-0023786 

0-00015397 

36 

00144 

0-0025879 

0-00016755 

37 

00148 

0 0028097 

000018190 

38 

00152 

0-0030437 

0-00019705 

39 

0 0156 

00032903 

0-00021302 

40 

00160 

00035650 

0 00022983 

41 

0-0164 

0-0038230 

000024751 

42 

0-0168 

0 0041096 

0-00026606 

43 

00172 

00044111 

0 00028553 

44 

00176 

0-0047250 

0-00030589 

45 

00180 

00050546 

0 00032725 

46 

00184 

0-0053991 

0-00034955 

47 

00188 

0-0057590 

0-00037285 

48 

00192 

00061344 

0-00039716 

49 

0-0196 

0-0065258 

000042250 

50 

0-0200 

0-0069335 

0-00044890 

51 

0-0204 

00073581 

0-00047638 

52 

0-0208 

00077799 

0-00050495 

53 

00212 

0-0082580 

0-00053464 

54 

00216 

0-00873438 

0-00056549 

55 

0-0220 

0-00922854 

0-00059748 

56 

0-0224 

00097412 

0-00063067 

















forbes’s blowpipe assay. 


5S9 


No. on 
scale 

Greatest diameter 
in inches 

Weight of globule in 
grains 

Weight of globule in 
grammes 

57 

0-0228 

0-0102725 

0-00066506 

58 

00232 

0-0108228 

0-00070021 

59 

00236 

0-0113922 

000073753 

GO 

00240 

00119815 

0-00077570 

61 

0-0244 

00125901 

0-00081513 

62 

0-0248 

00132119 

0-00085588 

63 

0-0252 

0-0138901 

000089797 

64 

0-0256 

00145440 

0-00094141 

65 

0 0260 

00152311 

0 00098623 

66 

0-0264 

00159472 

000103245 

67 

0-0268 

0-0166828 

0-00108010 

68 

0-0272 

0-0174414 

0-00112918 

69 

0-0276 

0-0182220 

000117974 

70 

0-0280 

0-0190256 

000123177 

71 

0-0284 

0-0198529 

0 00128535 

72 

0-0288 

00207035 

0 00134041 

73 

0-0292 

0-0215782 

000139704 

74 

0-0296 

00224469 

0-00145525 

75 

0-0300 

00234010 

0-00151504 

76 

0-0304 

00243496 

0-00157645 

77 

0-0308 

00253224 

0-00163950 

78 

0-0312 

0-0263228 

0-00170422 

79 

00316 

0 0273484 

000177060 

80 

0-0320 

0-0284000 

0 00183869 

81 

00324 

0-0294789 

0-00190852 

82 

0-0328 

00305838 

0-00198008 

83 

0-0332 

00317162 

000205340 

84 

0 0336 

0-0328768 

0-00212851 

85 

00340 

0 0340649 

0-00220549 

86 

00344 

00349739 

0-00228400 

87 

0 0348 

0 0364422 

0 00285938 

88 

0-0352 

00378008 

0-00244730 

89 

0-0356 

0-0390138 

0-00253168 

90 

00360 

0-0404368 

0-00261797 

91 

00364 

00417943 

0-00270790 

92 

00368 

0 0431930 

0-00279642 

93 

0-0372 

0-0446162 

0-00288860 

94 

00376 

0-0460718 

0-00298279 

95 

0-0380 

00475573 

0-00307900 

96 

0 0384 

0 0465239 

0 00317728 

97 

0 0388 

00506249 

0-00327759 

98 

0-0392 

0-0522069 

0-00338020 

99 

00396 

0 0538215 

0 00348452 

100 

0-0400 

0-0554688 

0-00359138 


Cupellation Loss .—This term is applied to indicate a 
minute loss of silver, unavoidably sustained in the process of 
cupellation, which arises from a small portion of that metal 
being mechanically carried along with the litharge into the 
body of the cupel. The amount of this loss increases with 
the quantity of lead present in the assay (whether contained 
originally in the assay or added subsequently for the 



















590 


THE ASSAY OF SILVER. 


purpose of slagging off the copper, Ac.); it is relatively 
greater, as the silver globule is larger, but represents a 
larger percentage of the silver actually contained in the 
assay, in proportion as the silver globule obtained diminishes 
in size. It has, however, been experimentally proved that, 
in assays of like richness in silver, this loss remains constant 
when the same temperature has been employed, and similar 
weights of lead have been oxidised in the operation. 

In the blowpipe assay this loss is not confined to the 
ultimate operation of cupellation, but occurs, though in a 
less degree, in the concentration of the silver-lead, and in 
the previous scorification of the assay, had such operation 
preceded the concentration. The total loss in the blow¬ 
pipe assay is found, however, to be less than in the ordinary 
muffle assay, since in the latter case the whole of the oxi¬ 
dised lead is directly absorbed by the cupel. 

In mercantile assays of ore it is not customary to pay 
attention to the cupellation loss, and the results are usu¬ 
ally stated in the weight of silver actually obtained. Where, 
however, great accuracy is required, especially when the 
substances are very rich in silver, the cupellation loss is 
added to the weight of the silver globule obtained, in order 
to arrive at the true percentage. 

The amount to be added for this purpose is shown in 
the annexed table, which is slightly modified from Platt- 
ner’s. 

The use of this table is best explained by an example, 
as the following:—An assay to which there had been 
added, in all, five times its weight of assay lead, gave 
a globule of silver equivalent to six per cent. Upon re¬ 
ferring to the table, it will be seen that the cupellation loss 
for this would be (TOT ; consequently the true percentage 
of silver contained in the assay would be G OT. This table 
is only extended to whole numbers, but fractional parts can 
easily be calculated from the same. 

When the globules of silver are so minute that they 
cannot be weighed, but must be measured upon the scale, 
the cupellation loss should not be added, since, as a rule, it 
would be less than the difference which might arise from 



forbes’s blowpipe assay. 


591 


Actual percentage 
of silver found by 
assay 

Cupellation loss, or percentage of silver to be added to the actual per¬ 
centage found by assay in order to show the true percentage of silver 
contained in same. The entire amount of lead in or added to the assay 
being the following multiples of the original weight of assay :— 

1 

2 

3 

4 

5 

6 

8 i 

11 

13 

kT 

99 - 

99 - 

751 

5 ] ‘ 

0 25 

0-32 

0-39 

0-45 

0-50 






90 


0-22 

0-29 

0-36 

0-42 

0-47 

0-69 

0-83 




80 


020 | 

0-26 

0-33 

0-39 

0-44 

0-64 

0 - 75 




70 


0-18 

0-23 

0-29 

0-35 

040 

0-58 

068 

0-82 



60 


016 

0-20 

0-26 

0-30 

0-36 

0-52 

0-61 

0-74 



50 


0-14 

0-17 

0-23 

0-26 

0-32 

0-46 

054 

0-65 



40 


012 

045 

0-20 

0-22 

0-27 

0-39 

0-46 

0-55 

0-62 


35 


Oil 

0*13 

0-18 

0-18 

0-25 

0-36 

0-42 

0-50 

0-57 


30 


o-io 

0-12 

0-16 

016 

0-22 

0-32 

0-38 

0-45 

0-51 


25 


0 09 

0-10 

0-14 

014 

0-20 

0-29 

0-34 

0-40 

0-45 


20 


0-08 

0-09 

012 

0-12 

0-17 

0-25 

0-29 

0-35 

039 

0-45 

15 


007 

0-08 

0-10 

0-11 

015 

0-20 

0-23 

0-28 

0-32 

0-37 

12 


006 

0-07 

0-09 

0-10 

0-13 

017 

0-19 

0-23 

0*26 

0-32 

10 


005 

0-06 

0-08 

0-09 

Oil 

015 

0-17 

0-20 

0-23 

0-27 

9 


0-04 

0 05 

0-07 

0-08 

0-10 

0-14 

016 

0-18 

021 

0-25 

8 


0-03 

004 

0-06 

0-07 

009 

013 

0-15 

016 

0-18 

0-22 

7 


0-02 

003 

0-05 

006 

0-08 

0-12 

013 

014 

0-16 

0-20 

6 


0-01 

002 

0-04 

005 

0-07 

010 

0-11 

0-12 

014 

0-17 

5 



001 

003 

004 

0 06 

0-09 

0-10 

Oil 

0-12 

0-14 

4 




0-02 

003 

0 05 

0-07 

0-08 

0-09 

0 10 

0-11 

3 




0-01 

002 

0-04 

005 

006 

0-07 

0-08 

0-09 

2 





001 

0-03 

004 

0-04 

0-05 

0-06 

0-07 

1 






' 001 

1 

0-03 

1 

003 

004 

004 

0-05 


errors of observation likely to occur when measuring their 
diameters upon the scale. 

In the case of beginners, it will be found that the 
cupellation is usually carried on at too high a temperature, 
and that thereby a greater loss is occasioned than would 
be accounted for by the above table. After some trials 
the necessary experience will be acquired in keeping up 
the proper temperature at which this operation should be 
effected. 

It now becomes necessary to consider in detail the pro¬ 
cesses requisite for extracting the silver contents (in com¬ 
bination with lead) from the various metallic alloys of 
silver which are met with in nature or produced in the 
arts. 

In considering these, the following classification of the 
substances will be found convenient:— 













































592 


THE ASSAY OF SILVER. 


I. Metallic Alloys. 

A. Capable of direct Cupellation. 

a. Consisting chiefly of lead or bismuth : silver-lead and 

argentiferous bismuth, native bismuthic silver. 

b. Consisting chiefly of silver : native silver, bar silver, test 

silver, precipitated silver, retorted silver amalgam, 
standard silver, alloys of silver with gold and copper. 

c. Consisting chiefly of copper: native copper, copper ingot, 

sheet or wire, cement copper, copper coins, copper- 
nickel alloys. 

B Incapable of direct Cupellation. 

a. Containing much copper or nickel, with more or less 

sulphur, arsenic, zinc, &c.; unrefined or black copper, 
brass, german silver. 

b. Containing tin : argentiferous tin, bronze, bell metal, 

gun metal, bronze coinage. 

c. Containing antimony, tellurium, or zinc. 

d. Containing mercury : amalgams. 

e. Containing much iron: argentiferous steel, bears from 

smelting furnaces. 

A. Metallic Alloys capable of direct Cupellation. 

a. Consisting chiefly of Lead or Bismuth. —In determining 
the silver contained in these alloys, it is only requisite to 
place a clean piece of the same, weighing about from one to 
ten grains according to its probable richness in silver, upon 
a cupel of coarse bone ash, and proceed by concentration 
and cupellation exactly as has been already described under 
these heads. 

Should the substance be not altogether metallic, or not free 
from adherent slag, earthy matter, or other extraneous matter, 
it should previously be fused on charcoal with a little borax in 
the reducing blowpipe flame, and the clean metallic globule 
then removed from the charcoal, and treated as before. In 
order to remove the globule from the inherent borax glass, it 
may be allowed to cool, and then detached ; or, after a little 
practice, it will be found easy, by a quick movement of the 
charcoal, to cause the globule, still melted, to detach itself 
completely, and drop on the anvil in the form of a single 
somewhat flattened globule, without suffering any loss of 
lead adhering to the charcoal. 

In the case of argentiferous bismuth alloys the process is 
carried on in all respects the same as if silver-lead were 


593 


FOKBES’S BLOWPIPE ASSAY. 

being treated. As, however, the bismuth globule is very 
brittle, care must be taken when separating the concen¬ 
trated globule from the litharge, as, if not carefully done, 
a loss may easily be sustained from a portion of the globule 
remaining behind adherent to the litharge. It is better, 
therefore, to remove the litharge by degrees from the 
globule with the aid of the forceps. 

Argentiferous bismuth, free from lead, when cupelled 
alone, invariably leaves a globule of silver, having a dull 
frosted surface. If, however, at the end of the operation a 
small quantity of lead to a grain) be added, and fused 
along with it, the silver globule then obtained will be 
perfectly bright and free from all bismuth. 

In the case of native bismuthic silver it is advisable to 
fuse the previously weighed mineral with a little lead and 
borax glass on charcoal in the reducing flame, so as to free 
it from any adherent earthy matter, and then proceed by 
concentration and cupellation, as before described. 

b. Consisting cliiefiy of Silver *: native silver , bar, test , and 
precipitated silver , retorted silver amalgam , standard silver , 
silver coin , and other alloys of silver with gold and copper .— 
These alloys may be at once fused with lead on the cupel 
itself, and the operation finished as before described. In 
general, however, it is better to fuse the weighed assay 
previously with the requisite amount of pure lead and a 
little borax-glass, say from a quarter to half the weight of 
assay, in the reducing flame at a low heat on charcoal until 
the globule commences to rotate. This ensures the having 
a perfectly clean button of silver-lead, which is then cupelled 
in the ordinary manner. 

In most cases the quantity of lead to be added need not 
exceed that of the weight of the alloy, but when several 
percentages of copper are present in the assay, as in case of 
many coins, &c., the lead should be increased to some three, 
or even five, times the weight of the assay in proportion to 
the amount of copper actually contained in the substance 
under examination, and which will be treated of more at 
length under the head of copper-silver alloys. 

When no more lead has been added to the assay than 

Q Q 



594 


THE ASSAY OF SILVER. 


its own weight, the cupellation may be concluded in one 
operation by inclining the stand, and so moving the globule 
on to a clean part of the cupel; but when more copper 
is present, it is preferable to concentrate first and cupel 
subsequently, in order thereby to reduce the cupellation 
loss to its minimum. 

In the concentration as much copper as possible should 
be slagged off with the lead, which is effected by inclining 
the cupel somewhat more than usual, so that its surface 
may be less covered up with the litharge and exposed as 
much as possible to oxidation, by which means the litharge, 
as it forms, is enabled to carry off more of the copper con¬ 
tained in the silver-lead. 

Should the silver globule after cupellation show indica¬ 
tions of still containing copper, as before noticed, when 
treating of cupellation, a small quantity of lead must be 
fused along with it, and the cupellation finished as usual. % 

As at the present time no means are known by which 

silver can be separated from gold by the use of the blow¬ 
pipe, in all cases of alloys containing gold, this metal 

remains to the last along with the silver, and the result in 

such cases always indicates the combined weight of both 
these metals contained in the alloy under examination. The 
employment of tlie humid assay must be resorted to for 
effecting their separation. 

c. Containing chiefly Copper: native copper , ingot , wire , 
or sheet copper , cement copper , copper coins , copper-nickel 
alloys. —Under the most favourable conditions in cupella¬ 
tion, the amount of lead requisite, when converted into 
litharge, to slag of one part of copper along with it as 
oxide, amounts to between seventeen and eighteen times its 
weight. In the blowpipe assay it is usual to add to any 
cupriferous alloy an amount of pure lead equal to twenty 
times the amount of copper contained in the alloy, in order 
to ensure the whole of the copper being separated in the 
litharge. In the case of nickel the amount of lead required 
is somewhat less than with copper, but in practice the same 
amount of lead may be employed. 

When the copper is quite clean the requisite amount of 


forbes’s blowpipe assay. 


595 


lead may be added to it in a single piece on the cupel, fused 
and cupelled as usual, after previous concentration of the 
silver-lead to a small-sized globule. 

It is generally found, however, that traces of iron, slag, 
gangue, or other foreign matter, are present; and, conse¬ 
quently, it is usually advisable to fuse the assay along with 
the requisite amount of lead, and about one half its own 
weight of borax-glass in the reducing flame, until the whole 
of the substance is seen to have perfectly combined or 
alloyed with the lead, and the globule has entered into brisk 
rotation, whilst at the same time no detached metallic 
globules are seen in the borax-glass. 

The concentration of the silver-lead and cupellation are 
then conducted as usual, taking care when concentrating 
to incline the cupel-stand so as to expose as much as possible 
of the metallic surface of the melted globule to the oxidising 
action of the air, with a view of enabling the litharge 
whilst forming to carry off as much copper along with it as 
possible. 

Should the silver globule obtained after cupellation spread 
out, or appear to the eye more flattened than usual with 
globules of pure silver, it indicates that some copper still 
remains, and a small piece of assay lead (I to 1 grain 
weight) should be placed alongside it whilst still on the 
cupel, fused together, and the cupellation finished on a clean 
part of the same cupel as usual. 

Precipitated or cement copper, especially that which is in 
the crude state, and has not been melted and run into ingots, 
is often very impure, containing so much iron, lead, arsenic, 
earthy matter, &c., as not to admit of direct cupellation, 
and in such case should be treated as pertaining to class 
B. a. 

B. Metallic Alloys incapable of direct Cupellation. 

a. Containing much Copper or Nickel , with frequently some 
little sulphur , arsenic , zinc , iron , cohalt , fyc., as unrefined or 
black copper , brass , German silver , <fc. —As the presence of 
these extraneous matters would interfere with the cupella¬ 
tion, either by causing a loss of silver-lead projected from 

q q 2 


596 


THE ASSAY OF SILVER. 


the cupel upon the evolution of the volatile substances 
present, or by forming oxides which could not be absorbed 
by the cupel, it is necessary to eliminate such substances by 
a scorification with borax on charcoal, previous to concen¬ 
tration or cupellation. 

In the case of unrefined and black copper, the portion 
used in the examination is placed in the scoop with twenty 
times its weight of assay lead, and its own weight of pow¬ 
dered borax-glass, mixed with the spatula, and transferred 
to a soda-paper cornet. It is then fused on charcoal in 
the reducing flame, which should be constant and uninter¬ 
rupted, until all particles have completely united, and a 
brisk rotation sets in, which is kept up for a short time, 
when the silver-lead globule, which should appear bright on 
the surface after cooling, is concentrated and cupelled pre¬ 
cisely as is directed under A. c. By this preliminary scori¬ 
fication the sulphur, arsenic, and zinc are volatilised, and 
any lead, cobalt, or iron slagged off into the borax-glass. 

In the assay of brass and German silver, the quantity 
employed is fluxed with its own weight of borax-glass, but 
only requires ten times its weight of assay lead. The 
operation is commenced as before, but the globule is kept 
somewhat longer in rotation (always keeping the flame 
directed only on to the borax-glass), so as to allow the zinc 
present to be completely volatilised, which is evident when 
the surface of the silver-lead becomes bright, on which the 
heat is increased for a few moments to expel the last traces 
of that metal, and the silver-lead thus obtained is concen¬ 
trated and cupelled as before. 

The silver globule obtained from the cupellation of sub¬ 
stances rich in copper generally requires the addition of a 
small quantity of lead and re-cupellation (as before de¬ 
scribed), in order to ensure its freedom from copper. 

b. Containing Tin: argentiferous tin , bronze , bell and 
gun metal , bronze coinage , <fc. —Alloys of silver with other 
metals containing tin do not admit of being cupelled, since 
the oxide of tin formed by the oxidation of that metal is 
not absorbed by the bone ash of the cupel along with the 
litharge ; it consequently remains upon the surface of the 


FORBES’S BLOWPIPE ASSAY. 


597 


cupel, and if present in any quantity interferes with the 
operation. As tin is not volatile when heated on charcoal, 
either in the oxidating or reducing blowpipe flame, it can¬ 
not be so dissipated, and in consequence, the entire amount 
of tin contained in any alloy under examination must be 
removed by oxidation or scoriflcation from the silver-lead, 
previous to its being submitted to cupellation. 

For this purpose, 1 part of the stanniferous alloy is fluxed 
with from 5 to 15 parts granulated assay lead (according 
to the amount of copper suspected to be present in the 
alloy), 0*5 part anhydrous carbonate of soda, and 05 part 
pulverised borax-glass, made up as usual in a soda-paper 
cornet, and the whole at first gently heated in reduction 
flame until the soda paper is charred and the alloy has after¬ 
wards united with the lead to form a single globule, whilst 
the borax and soda have combined as a glass or slag in 

o < 

which the soda prevents the easily oxidisable tin becoming 
oxidised to any extent before a perfect alloy has been 
formed with the lead, which then contains the whole of the 
silver. 

As soon as this is effected, the blowpipe flame is altered 
to an oxidating one, and the metallic globule is kept at the 
point of the blue flame, which should touch it so as to 
cause the tin to become oxidised and be at once taken up 
by the glass surrounding it. 

Should, however, it be seen that minute globules of me¬ 
tallic tin made their appearance on the outer edge of the 
slag or glass,* the operation must be at once discontinued, 
and the assay allowed to cool; after cooling the metallic 
globule is detached from the slag surrounding it, and being 
placed in a cavity on charcoal, is fused in the reducing 
flame along with a small piece of borax-glass and afterwards 
treated with the oxidating flame exactly as before (and if 
necessary, which is seldom the case, unless when treating 
argentiferous block tin, this operation may again require to 
be repeated), until it is seen that the surface of the metallic 
silver-lead globule does not any longer become covered 

* This occurs when the flux has become so saturated with oxide of tin that 
it cannot take up any more. 



598 


THE ASSAY OF SILVER. 


with a crust or scales of oxide of tin, but presents a pure 
and bright metallic surface. 

The silver-lead globule is now quite free from tin, and 
can be cupelled and the amount of silver determined as 
usual. 

c. Metallic alloys containing much antimony , tellurium , or 
zinc : antimonial silver and argentiferous antimony , telluric 
silver , and argentiferous zinc. —Alloys of antimony with 
silver when treated on charcoal in the oxidating flame give 
off all their antimonv, leaving the silver behind as a metallic 
globule having a frosted external appearance ; telluric silver, 
on the contrary, however, when treated in a similar manner, 
only evolves a part of its tellurium, and even after cupella- 
tion with lead a small amount of tellurium generally remains 
behind alloyed with the silver. 

All these compounds may be assayed as follows :— 

One part of the alloy is placed in a soda-paper cornet 
along with 5 parts granulated assay lead, and 0 5 part pul¬ 
verised borax-glass, and fused in reducing flame until the 
globule and slag are well developed ; the oxidating flame is 
now directed on to the globule, causing the whole of the 
zinc, along with most of the antimony and part of the tellu¬ 
rium, to volatilise before the lead commences oxidising. 

. ® 
The last traces of antimony are removed with some difficulty, 

during which operation some portion of the lead becomes 
oxidised. On cooling, the globule is now separated from 
the slag and concentrated upon a coarse bone-ash cupel as 
usual, and if no tellurium were present in the concentrated 
silver-lead, this may now be cupelled as usual. 

If tellurium is present, as is seen by the concentrated 
globule of silver-lead possessing a dark-coloured exterior, it 
must be remelted with 5 parts assay lead and again concen¬ 
trated ; and these operations, if necessary, must be repeated 
until the surface of the concentrated globule is found to be 
clean and bright, as usual with pure silver-lead, when it may 
be cupelled fine and the silver globule weighed. 

It sometimes happens, even after all these precautions 
have been taken, that the silver globule after cupellation 
shows a crystalline, greyish-white, frosted appearance, from 


FORBES’S BLOWPIPE ASSAY. 599 

its still containing tellurium ; in such cases its own weight of 
assay lead (in one piece) should be placed beside it on the 
cupel, melted together, and the globule again cupelled fine 
on another part of the surface of the same cupel. In as¬ 
saying substances very rich in tellurium the results obtained 
are, however, not very satisfactory, and may be as much 
as one or two per cent, too low, even after employing all 
precautions. 

d. Compounds of Silver ivith Mercury: arquerite , native 
and artificial amalgams and argentiferous mercury. —The 
assay of these compounds is very simple. A weighed quan¬ 
tity of the liquid or solid amalgam is placed in a small bulb 
tube, and heated over the lamp very gradually in order to 
avoid spirting and to allow the mercury to volatilise quietly ;* 
the heat is increased by degrees as long as any mercury is 
driven off', and the residue is heated for some time at a red 
heat in order to drive off as much mercury as possible with¬ 
out fusing the glass or causing the residual silver to adhere 
to it. The mercury expelled condenses itself above the 
bidb on to the upper part of the tube, and by gently tapping 
will collect in globules, which by carefully turning the tube, 
unite and can be poured out of the tube ; after which the 
silver, left behind as a porous mass, may be removed from 
the tube, and after being fluxed with an equal weight of 
granulated assay lead and half its weight of borax-glass, 
must be fused on charcoal in the reducing flame, and the 
button, on cooling, cupelled as usual. Should, however, 
much copper have been present in the amalgam, a propor¬ 
tionately larger amount of assay lead is required to be 
added. 

When the argentiferous residue is extremely small, as is 
often the case when assaying argentiferous mercury, this 
may adhere firmly to the glass of the tube. On such occa¬ 
sions this part of the tube must be cut off with the adherent 
residue, and the whole fused in a strong reducing flame 


* In the case of solid amalgams, which often spirt very violently, this may 
he obviated by wrapping the assay in a small piece of tissue paper, and heating 
it in a blowpipe crucible, when all the mercury is given off quietly, leaving 
the silver behind. 


THE ASSAY OF SILVER. 


fiOO 

along with its own weight of granulated assay lead, and with 
half its weight of anhydrous carbonate of soda. Upon cool¬ 
ing, the globule of silver-lead thus obtained is cupelled as 
usual. 

e. Compounds chiefly consisting of Iron: argentiferous- 
steel ; cast-iron ; bears from smelting furnace. —Compounds 
consisting principally of iron with a small percentage of 
silver, although occasionally produced in the arts inten¬ 
tionally, as, for example, the so-called silver-steel, are com¬ 
monly found on the blowing-out of furnaces used in the 
smelting of silver and copper ores, and are frequently rich 
in silver, as is the case with the bears from the silver 
furnaces at Kongsberg in Norway. An alloy of iron with 
silver is occasionally also found appearing in small quantities 
on the surface of melted silver in the process of casting, and 
in some cases at least this may be due to the action of the 
melted silver on the iron rods used for stirring up the 
molten metal. 

As iron cannot be made to alloy itself with lead before 
the blowpipe, it becomes necessary to extract the silver by 
a more indirect process than is used in the case of other 
alloys containing that metal. In order to remove the iron 
the alloy must first be converted into sulphide of iron and 
silver, and to effect this the iron or steel must be reduced to 
powder, or fragments none greater than about a quarter of 
a grain in weight; for which purpose steel when hardened 
may require to be softened previously. 

One part of the finely-divided iron or steel is now mixed 
with 0*75 part sulphur, eight parts granulated assay lead, 
and one part pulverised borax-glass ; the mixture after being 
placed in a soda-paper cornet is carefully fused in a cavity 
on charcoal in the reducing flame, until the whole appears 
as a fluid globule containing both the lead and iron in com¬ 
bination with the sulphur. Without removing either this 
globule or the glass surrounding it from the charcoal, an 
amount of borax-glass in one or more fragments (in all about 
equal in weight to the original amount of iron employed), is 
now added (in order to combine with and slag off the whole 
of the iron), and fused along with the former globule, after 


forbes’s blowpipe assay. 


601 


Avliicli the whole is submitted to a strong oxidating flame 
until the impure lead globule shows itself protruding from 
the si a" 

O 

The charcoal is then inclined, so that the lead is alone 
subjected to the action of the outer flame, in order to vola¬ 
tilise the sulphur, and at the same time oxidise the iron 
which goes into the slag : this operation is continued until 
the globule of lead appears with a bright metallic surface ; 
should it on cooling, however, be found to possess a black 
colour, and to be brittle, it must be still further oxidised as 
before described. 

The silver-lead thus obtained will now be found to con¬ 
tain all the silver, and at the same time to be free from both 
iron and sulphur, and can be cupelled as usual. 

No notice is here taken of alloys of silver and gold, since 
these metals cannot be separated before the blowpipe by any 
process yet known ; and in all cases where gold may be 
present in an alloy, treated as here directed for obtaining its 
contents in silver, the gold also will be found to follow along 
with the silver, and must be parted from that metal by the 
humid method, in order to enable the true amount of silver 
present in the substance to be ascertained. 


THE ASSAY OF GOLD. 


t)0‘2 


CHAPTER XVI. 

THE ASSAY OF GOLD. 

For tlie purposes of assay, all substances containing gold 
may be divided into two classes, as in the case of silver. 

The First Class comprises all substances containing gold 
in a minute state of division; such, for instance, as those 
which, suitably pulverised, completely pass through a sieve 
of 80 holes to the linear inch. It often happens, however, 
that these substances contain fragments of gold of such 
magnitude as will not allow them to pass through the 
sieve : in such cases, that which passes through belongs to 
the first class, and that which remains on the sieve to the 
second class. 

The Second Class comprises all alloys of gold, native or 
otherwise. 

The name of substances belonging to this class is legion, 
for an extended examination shows that nearly every 
mineral substance contains more or less gold. The most 
common are—gold quartz, auriferous gossans, sulphides of 
iron (mundic), blende, copper pyrites, many antimonial 
minerals, galena, and nearly all the primitive rocks. All 
auriferous slags, amalgamation residues, and tailings, belong 
to this class. 

Assay of substances of the First Class .—This assay is 
conducted in precisely the same manner as that of the cor¬ 
responding silver class, which see. In case, however, the 
amount of gold present in the sample is small, as much as 
2,000 grains, with flux suitably increased, may be employed. 
In case any metallic gold is left in the sieve, its amount is 
to be calculated as that of silver (see pages 476 and 477). 

It may here be mentioned, that if silver or platinum 


SUBSTANCES OF THE SECOND CLASS. 


603 


coexist with the gold in the mineral subjected to assay, t 
will be found combined with the gold obtained by cupella- 
tion; and all gold so obtained must be submitted to the 
4 parting process,’ which see under the head 4 Assay of Auri¬ 
ferous Substances of the Second Class.’ It may here be 
mentioned also, that the metallic gold left on the sieve must 
be thus operated on, as well as that obtained by fusion of the 
sieved ore and consequent cupellation, before the calculation 
given at pages 476 and 477 be entered into. 

When gold is associated in quantity with quartz, its per¬ 
centage can be approximatively ascertained in the same 
manner as that of pure tin-stone when mixed with quartz 
(see pages 414 and 415). 'If possible, a fragment of the 
gold must be detached from the quartz, and its specific 
gravity taken : if this be not possible, and the gold is nearly 
fine, the number 19 may be adopted. It is better, however, 
to determine experimentally the specific gravity of both 
quartz and gold. 

Substances of the Second Class. 

Native gold. 

Aurides of silver (native). 

Gold and rhodium. 

Gold and palladium. 

Argentiferous telluride of gold. 

Plumbo-argentiferous telluride of gold. 

Sulpho-plumbiferous telluride of gold. 

Artificial alloys of gold. 

Native Gold and Aurides of Silver {Native), Au and 
AuAg n , are found in variously contorted and branched fila¬ 
ments, in scales, in plates, in small irregular masses, in the 
crevices or on the surface of common ferruginous and other 
quartz. In Devonshire, at the Britannia Mine, it has 
occurred in pipes or veins, and disseminated in a compact 
hard gossan, one specimen of which was found to contain 27 i 
per cent, of fine gold; or, as in Wales, it largely accom¬ 
panies blende and galena : it also occurs in a pyritous quartz ; 
it has been found in Scotland and Ireland. In the latter 


604 


TIIE ASSAY OF GOLD. 


locality it occurred in the beds of streams as small scales 
and rolled masses, and nearly up to the present time this 
has been the most frequent mode of occurrence; but now, 
however, by the aid of improved machinery, rocks and 
minerals containing a comparatively small quantity can be 
profitably worked; and from this source, the greatest part 
of the gold poured into commerce is now extracted. 


Composition of several varieties of Native Gold, by Boussin- 
gault, the chief part from Central America. 



Malpaso 

Llano 

La Baja 

Rio-Sucio 

Gold 

. 88-24 

88-58 

88-15 

87-94 

Silver 

. 11-76 

11-42 

11-85 

1206 


100-00 

100 00 

10000 

10000 


Ojas Anchas 

Trinidad 

Guano 

Otramina 

Gold 

. 84-50 

82-40 

73-68 

73-60 

Silver 

. 15-50 

17-60 

26-32 

26-60 


100-00 

100-00 

100-00 

100-00 

Gold 

Titiribi 

Marmato 

Transylvania 

Santa Rosa 

. 74-00 

73-45 

64-52 

64-93 

Silver 

. 26-00 

26-55 

35-48 

35 07 


loo-oo 

10000 

100-00 

100-00 


Specimens 

of Gold from Siberia, 

by Bose. 



Schabrowski, near 

Borushka, near 



Katherinenburg 

Nischen-Tagil 

Gold 

• 

. 98-76 

94-41 

Silver . 

• 

. . 00-16 

05-23 

Copper . 

• 

. 00-35 

00-39 

Iron . 

• 

. 0005 

00 04 



99-32 

100 07 



Berescoff 

Katherinenburg 

Gold 

#• 

. 93-78 

93-34 

Silver . 

• 

. 5-94 

6-28 

Copper . 

• 

•08 

•06 

Iron 

• 

•00 

•32 



99-80 

100-00 



Crascewo Nicolajeusk, 

Perroc Powlowsk, 



near Miask 

near Berescoff 

Gold 

• 

. 92-47 

92-60 

Silver . 


. . 7-27 

7-08 

Copper . 

• 

•06 

•18 

Iron , 

• 

•08 

•06 



99-88 

99-92 



Borushklei 

Alexander Andrejeusk, 
near Miask 

Gold « 

• 

. 90-76 

87-40 

Silver . 

• 

. 9-02 

1207 

Copper. 

• 

•09 

•09 



99-87 

99-56 














GOLD FROM DIFFERENT COUNTRIES. 


605 


Gold from Senegal, by D’Arcet. 

Gold . . . ... . . . 86-97 

Silver.10-53 

97-50 


Gold from Brazil, by D’Arcet. 

Gold.94-00 

Silver.5-85 

99-85 

Gold from Anamaboe, Africa, by Henry . 

Gold.98-06 

Silver.1-39 

• lion ........ '1») 

“99-60 


Gold from California, by Henry . 



1. 

0 

• 

Gold . 

86-87 

88-75 

Silver . . . ‘ . 

12-33 * 

8-88 

Copper. 

•29 

•85 

Iron ..... 

•54 

traces 

Silica. 

•00 

1-40 


10003 

99-88 

Gold from California, by 

Teschemacher. 

Oold * • • • • 

• • 

. 90-33 

Silver .... 

• • 

. 6-80 

Oxide of iron 

• • 

. 1-10 

Sand. 


•66 

...» 


98-89 


Gold from Australia, by Henry . 


Gold . 
Silver 
Iron . 


95-68 

3-92 

_yl6 

99-76 


Gold from Devonshire and Wales by the Author. 

The author lias received two specimens of gold, one from 
Wales, and the other from the Britannia Mine, Devon; and 
found both to be absolutely line gold. 

Gold and Rhodium .—This compound was discovered by 
M. Andre del Bio among some gold ores in Mexico. It has 
a gold colour, and contains variable proportions of rhodium; 
the mean, however, is 34 per cent. 





606 


THE ASSAY OF GOLD. 


Gold and Palladium. —The following is the composition 
of this alloy :— 


Gold 

Palladium . 
Silver 


. 85-98 
. 9-85 

. 4.17 

100-00 


Argentiferous Telluride of Gold (AgTe 2 + 3AuTe 6 ). 
Composition :— 

Gold 80 

Silver.10 

Tellurium. t6 

56 


Plumb o-argentiferous Telluride of Gold (probable formula, 
AgTe 2 4 3 AuTe 3 + 2PbTe 2 ). 

Composition :— 


Gold . 
Silver 
Lead . 
Tellurium 
Sulphur 


26’75 

8-50 

19-50 

44-75 

•50 

100-00 


Sulpho-plumbiferous Telluride of Gold (probable formula 
AuTe 3 + 4PbTe 2 + 2PbS). 

Composition :— 


Gold . 


• 

• 

• 

• 

. 90 

Silver . 





• 

•5 

Lead . 





• 

. 54-0 

Copper 





• 

. 1*8 

Tellurium 





• 

. 32-2 

Sulphur 





• 

. 30 

100-0 


Artificial Alloys of Gold. —The only one of these alloys 
which will be specially noticed here, is the standard gold of 
this realm. It is composed of 22 parts of fine gold and 2 
parts of alloy (copper), constituting 22 carat or standard 
gold. 


General Observations on the Assay of Gold Alloys. 

Cupellation , Gold and Lead. —The cupellation of the 
alloys of gold and lead is conducted in a similar manner to 
those of silver and lead. It presents even less difficulty, 











ASSAY OF GOLD ALLOYS. 


607 


and requires less precaution, because it is not so volatile, 
and because it has a less tendency than silver to penetrate 
into the cupel, and the button is less subject to throw pieces 
out of the cupel. These cupellations take place at a higher 
temperature than those of silver, and we need not be afraid 
of giving a good heat at the moment of brightening : the 
gold is but the purer. 

Mr. Makins made the following statements on certain 
sources of loss of precious metals in some operations of assay¬ 
ing before the Chemical Society, January 19, 1860. When 
making a large number of assays of gold, and also estimating 
the silver, under circumstances which required that an 
extraordinary degree of heat should be employed, Mr. Makin 
was struck with the great loss of gold and silver. Satisfied 
that it was not entirely owing to ‘ cupel absorption ’ he 
examined the contents of the iron flue of the furnace, which 
had only been used for the cupellation of gold assays, to see 
if any of the precious metals had been volatilised. Under 
the microscope the apparently carbonaceous matter from 
the flue showed yellow masses of oxide of lead, nodules of 
suboxide of copper, and minute grains of silver mixed witli 
carbonised matter containing small grains of unburnt fuel. 
On analysis the metallic matters present were found to be 
oxide of lead mixed with small portions of gold, silver, and 
oxide of copper. The metals were extracted by lead in the 
usual way, and the button obtained by scorification was sub¬ 
jected to cupellation. The gold and silver were then parted, 
and the proportions of each in 1,000 grains were found to 
be:— 


Gold ........ 0087 

Silver ....... 0703 

Gold and Copper, proportion of Lead .—The alloys of gold 
and copper are cupelled like the alloys of gold and silver; 
but as copper has a very great affinity for gold, it is neces¬ 
sary to use a larger proportion of lead to ensure its oxidation 
when combined with gold than when united with silver. 
This proportion varies according to the standard and the 
temperature. It is admitted that for the same standard 


608 


T1IE ASSAY OF GOLD. 


there must, under similar circumstances, be twice as much 
lead used in the cupellation of gold as for that of silver. 
Thus, 14 parts, at least, ought to be employed in common 
furnaces for an assay of gold coin which contains 01 of 
copper. There is no inconvenience in employing a little 
more, as it does not increase the loss of gold. However 
great the proportion of lead may be that is added to the 
cupreous gold for the purpose of cupellation, the button 
retains always a very small quantity of copper, which a 
fresh cupellation does not free it from, and which occasions 
what is termed the surcharge. This surcharge being very 
slight, can be neglected in assays of minerals; but it is 
necessary to take notice of it in the assay of alloys. But it 
is known that the presence of silver much facilitates the 
separation of copper from gold, and it is rare that an alloy 
of cupreous gold does not contain a little silver, which must 
be separated: and when that is not the case, a small 
quantity of that metal can be introduced into the alloy, so 
as to be in about the proportion of 3 parts to 1 of gold. 
When an assay is to be made of an alloy of gold and copper, 
a sufficient quantity of silver is to be added to fulfil this 
condition according to the presumed standard, which is 
determined approximatively by a preliminary assay, and 
then cupelled with lead. 

The examination on the touch-stone is based upon the 
fact, that the richer an alloy is in gold the more clearly 
does a streak drawn with it on a black ground present 
a pure gold-yellow colour, and the less is it attacked 
by pure nitric acid or by a test acid. This test acid consists 
of ninety-eight parts pure nitric acid of 1*34 spec. grav. 
(37° Beaume), two parts pure hydrochloric acid of 1T73 
spec. grav. (21° B.), and twenty-five parts distilled water. 
To judge of the richness of the alloy to be examined, its 
streak is compared with marks drawn with alloys (the touch- 
needles) whose richness is accurately known. In order to 
get correctly the streak of the alloy to be tested, the surface 
of the metal must first be somewhat filed away, since this 
may be impure, or, as with coins and jewelry, it may have 
been made somewhat richer by boiling with acid, and the 


601) 


EXAMINATION ON TIIE TOUCHSTONE. 

so-called colouring of the goldsmith, and a clean fracture 
is rarely to be obtained. Five series of prepared touch- 
needles are required, The first series consists of copper 
and gold, and is called the red series , and the proportion of 
gold increases by half carats in the successive needles. The 
second series, the white series , contains needles of gold and 
silver, in which the proportion of gold likewise increases by 
half carats. The third series, a mixed one , contains needles 
in which the quantities of silver and copper are equal, and 
the proportion of gold also increases by half carats. The 
fourth consists also of needles for a mixed series, in which 
the silver is to the copper as 2:1, and the gold increases 
by half carats ; and the fifth is also formed of needles for a 
mixed series, in which the quantity of silver is to that of 
the copper as 1 : 2. Moreover, in mints and stamping 
bureaux, alloys are used which correspond precisely to the 
legal standards. The testing upon the touchstone begins by 
determining to which series the alloy to be examined belongs. 
Then those touch-needles are rubbed against the stone whose 
marks most nearly approximate in colour to that of the alloy. 
The marks must form a thin continuous layer. A drop of 
pure nitric acid is now placed upon them with a glass rod, and 
its comparative effect observed. The acid is allowed to work 
a short time, and then wiped off, in order to see whether the 
streak appears unchanged, or whether it has more or less dis¬ 
appeared. The test acid above is also used. This is so com¬ 
posed that it does not work at all upon an alloy containing 
eighteen carats and more of gold, and with such an alloy the 
streak, after using the acid, will not be wiped off with a fine 
linen rag, provided that stone and acid had a temperature of 
10 to 12° C. Pure nitric acid produces almost no effect upon an 
alloy of fifteen or sixteen carats fine, and over. The testing on 
the touchstone can indeed make no pretension to accuracy, 
especially where the amount of gold is small, but it yields 
sufficiently useful results for a preliminary test. It requires, 
however, a sharp and ver}^ practised eye. Moreover, the 
preparation of the touch-needles is wearisome, as the re¬ 
quired proportion is not always quickly reached, nor are 
good malleable alloys always obtained. The touchstone, 

R R 


G10 


TFIE ASSAY OF GOLD. 


therefore, is in general only used where frequent gold assays 
are to be made of alloys varying in richness, or where (as fre¬ 
quently with gold plate) an examination on the touchstone 
will suffice. 


Table for proportion - of Lead to be employed in the 

CuPELLATION OF CtOLI) AND COPPER. 


Gold in Alloy 

] 000 tli o usan d tli s 


noo 



800 


>> 

700 



000 



500 


V 

400 ^ 

300 



200 \ 

V 

100 



50 J 




Ratio of lead in 
Lead required the assay to the 
copper, &c. 


1 part 


10 parts 

100,000 : 

1 

16 

)) 

80,000 : 

1 

22 

yy 

73,333 : 

1 

24 

yy 

00,000 : 

1 

20 

V 

52,600 : 

1 


56,600 : 

1 



48,571 : 

1 

34 

V 

42,500 : 

1 


37,777 : 

1 


Kandelhardt gives the ratio in the following table :— 


Gold in 1000 parts 




Quantity of lead required 

1000 tine gold 



. 8 times the 

weight of the all^y 

980 — 020 . 



. 12 

yy 

V 

V 

920 — 875 . 



. 10 

V 

yy 


875 — 750 . 



. 20 

yy 

yy 


750 — 000 . 



. 24 

V 

yy 


600 — 350 . 



. 28 

yy 

yy 


350 — 0 . 



. 32 


yy 



Gold , Silver , Platinum , and Copper .—The presence of 
platinum in an alloy renders the separation of the oxidisable 
metals, more especially copper, very difficult by cupellation. 
It appears, indeed, that it would be almost impossible to 
arrive at it, if the alloy of copper contained nothing but 
gold and platinum. It is necessary that silver be present at 
the same time. When this metal is absent, it is requisite to 
add a quantity of it, which ought to be equivalent to double 
the weight of the gold and platinum united, and cupel at the 
strongest heat which can be obtained in a good muffle with 
a suitable proportion of lead. This proportion varies much 
according to the composition of the alloy, and the tempera¬ 
ture at which the operation is carried on. 

Experience has shown that the copper can be more com¬ 
pletely separated, and less silver lost, by cupelling at a high 
temperature, with the least possible quantity of lead, than 













ASSAY OP GOLD ALLOYS. 


611 


by employing more lead, and working at a lower tempera¬ 
ture. M. Ohaudet has made several assays, in order to 
determine the proportion of lead required for the cupella- 
tion of the three following alloys 



1 . 

2. 

3. 

Gold. 

. 0100 

0020 

0-005 

Platinum .... 

. 0100 

0-200 

0-300 

Silver .... 

. 0-250 

0-580 

0-595 

Copper .... 

. 0-550 

0-200 

0100 

And has found, for the first, 

that by 

employing 

20 par 


lead the separation is very nearly complete ; but that at a 
higher temperature there is a loss of silver; and in order 
to render the assay correct, it must be cupelled at the 
latter temperature, with only 14 of lead ; for the second, 
8 of lead, at a high temperature ; and for the third 30 
parts of lead are necessary, at the same high temperature of 
the muffle; but it is almost impossible to separate all the 
copper, and no advantage can be obtained by increasing the 
quantity of lead. When almost the last traces of the copper 
, are separated, the button must be cupelled afresh, with a 
small quantity of lead; but a small quantity of silver is 
nearly always lost. In all cases, in order that no lead shall 
remain, it is necessary to leave the assay button some few 
minutes in the muffle, after cupellation is finished. 

The alloys of gold and silver which contain platinum 
show, either by cupellation or parting, certain characters 
which prove the presence of that metal. If the assay be 
not heated very strongly, it does not pass, and the button 
becomes fiat: this effect becomes very sensible when the 
platinum is to the gold as the proportion of 2 to 100. 
Under the same circumstances, the nitric acid solution pro¬ 
ceeding from the parting is coloured straw-yellow. At the 
moment an assay of an alloy containing platinum terminates, 
the motion is slower, and the coloured bands are less 
numerous, more obscure, and remain a much longer time 
than when there is no platinum : the button does not un¬ 
cover, and the surface does not become as brilliant as that 
of an alloy of gold or silver, but it remains dull and 
tarnished. When the assay is well made, it is to be re¬ 
marked that the edges of the button are thicker and more 

R R 2 



G12 


THE ASSAY OF GOLD. 


rounded than in ordinary assays, and it is of a dull white, 
approaching a little to the yellow; and lastly, its surface is 
wholly or in part crystalline. These effects are sensible 
even when the gold does not contain more than 0*01 of 
platinum. When the alloy contains more than 10 parts of 
platinum to 90 of gold, the annealed cornet produced in 
the parting process is of a pale yellow, or tarnished silver 
colour. 

Gold alloyed with Silver. —The separation of gold from 
silver is termed parting. Parting is not only used to sepa¬ 
rate silver from gold, but for the separation of other metals, 
such as copper, when cupellation does not separate it 
entirely. Parting by the wet process is carried on by the 
means of nitric acid, aqua regia , or sulphuric acid. 

When an alloy of gold and silver has been reduced by a 
flatting mill to very thin plates, it is sufficient that it con¬ 
tains of silver to 1 of gold in order that the parting may 
be effected completely by nitric acid, and takes place much 
less easily when the silver in the alloy is in larger propor- • 
tion : but when this proportion exceeds 3 parts of silver for 
1 of gold, then the latter is obtained in leaves so fine, that 
there is risk incurred of losing some in the subsequent 
manipulation, and even by the act of boiling the acid 
liquid. 

We must always, therefore, when-a very exact assay is 
required, contrive that the alloy shall contain a little less 
than 3 parts of silver to 1 of gold; a proportion which 
long experience has demonstrated to be the best. If the 
alloy contain less than 2\ 2 °f silver to 1 of gold, the silver 
does not wholly dissolve, because there is a part of it so 
enveloped in the gold that the strongest acid does not act 
on it.* 

Inquartation. — The operation by which the alloy is 
brought to this standard is termed quartation , or inquar- 
ation. It consists in fusing the alloy in a cupel, with 2 
parts of lead and the quantity of fine silver, or fine gold, 
necessary to bring it to the desired composition. This 

* Pettenkoffer and others have shown that less than two parts of silver will 
suffice, and be even advantageous. 


TIIE OPERATION OF INQUARTATION. 


G13 


quantity is estimated according to the approximative deter¬ 
mination of the standard of the alloy, which ought to be 
made either by means of a preliminary assay, as hereafter 
described, or by means of the touchstone. If we do not 
employ the whole of the alloy the assay will not be exact, 
because the gold and silver are not always found distributed 
in an uniform manner ; at least, every time it is not poured 
into a cold ingot mould. 

Operation .—The cupelled and quartated button is flattened 
on an anvil and annealed, in order to soften it. It is lami¬ 
nated to give it a certain thickness, and is then annealed 
afresh, and rolled into a cornet or spiral around the quill of 
a pen. It is necessary that the alloy should be reduced to a 
suitable thickness, on the one hand, in order that the silver 
may be dissolved completely: and, on the other, that the 
plate of gold may remain whole after the operation. The 
following is that which experience has proved best. The 
quantity of matter operated upon, or taken for the assay, 
should be about 12 grains; and the alloys resulting from 
these 12 grains, and the silver, employed in the inquartation 
into a plate of from 18 to 20 lines in length and 4 or 5 in 
breadth. 

The cornet for assay is placed in a glass matrass, capable 
of containing about three ounces of water ; pure nitric acid 
is added at different times, and heat applied. When all the 
silver is dissolved, it is washed by decantation with water ; 
the matrass is reversed into a small crucible, the cornet falls 
out and is dried. In this state the cornet is very fragile, 
and of a dull red colour; it is annealed in a muffle, and 
heated gradually without fusion. It becomes thereby much 
contracted, and acquires a metallic lustre, and so much 
solidity that it can be weighed without fear of breaking it. 
Its weight can be ascertained in the assay balance. 

Tliere are many ways of employing nitric acid. Formerly 
21 ounces (thirty-live times the weight of the alloy) of 
nitric acid (IT5 sp. gr.) was poured upon the inquartated 
cornet, and boiled gently for fifteen or twenty minutes, 
the liquid decanted and replaced by 1^ of acid (1*24 or 
1*26), twenty-four times the weight of the alloy, boiling for 


G14 


TI1E ASSAY OF GOLD. 


twelve minutes, then decanting and washing, Ac. Vauque- 
lain advised, in his ‘Manuel de 1’Essayeur,’ to pour on 
the quartated cornet—the weight of the assay being 7*7 
grains—554 to 770 grains of nitric acid (1*16 sp. gr.), 
which ought to fill the matrass half or two-thirds, and boil 
gently for twenty, or twenty-two minutes at most, to decant 
and replace the liquid by 500 to 800 grains of acid (1*26 
sp. gr.), and to boil for eight or ten minutes. The assay is 
to be acted on always twice, because, if we employ at 
once very strong acid, the action will be too brisk, and the 
cornet might be broken or carried out of the matrass, and, 
on the other side, the acid of 1*16 sp. gr. cannot dissolve 
the last portions of silver, which are very difficult to 
separate from the gold. 

Surcharge .—It is remarked that by following this method 
the cornet always retains a small quantity of silver, so that 
fine gold submitted to quartation and parting always weighs 
more after than before the operation. The augmentation 
of weight which it undergoes is termed the surcharge ; this 
surcharge is commonly from 0*001 to 0*002. M. Chaudet 
has found means to avoid it. In order to do so, pour on 
to the quartrated cornet nitric acid of 1*16 sp. gr., and 
heat for three or four minutes only ; replace this acid by 
acid at 1*26 sp. gr., and boil during ten minutes; decant 
and make a second boiling with acid at 1*26 sp. gr., which 
boil for eight or ten minutes. The assay requires but from 
twenty to twenty-three minutes, and, according to M. 
Chaudet, gives perfectly pure gold. 

The following statements referring to this subject were 
made in the Chemical Society on January 19, 1860 :_ 

A source of loss occurs in parting operations and refining 
on the large scale, from the solution of gold in nitric 
acid, even when it is quite free from hydrochloric acid, in 
consequence of the formation of nitrous acid. Mr. Field, 
the Queen’s assay master, had a bottle which was thickly 
coated with gold deposited from nitric acid which had been 
used in parting operations. Sir John Herschel thought 
that the gold might have been suspended in the acid ; but 
the fact that the bottle was pear-shaped, and was uniformly 


ASSAY OF AURIFEROUS ORES. 


615 


coated with the metal, proved that it must have separated 
from a solution. To ascertain the amount of loss from this 
source in ordinary assay operations, Mr. Makin took four 
specimens of pure gold accurately weighed, added the usual 
proportions ol line silver and lead, and then cupelled them. 
The resulting buttons were rolled, coiled, and parted with 
nitric acid, the cornets being boiled in two acids of different 
strengths a different number of times. Calling the weighings 
before the operation 1000, the results were as follows :— 


1. Boiled in acid twice . 

2. ,, three times . 

3. „ four „ 

4. ,, five ,, 


999-6 

999-2 

998-7 

997-9 


The loss is thus seen to increase as the boilings are multi¬ 
plied. 

When silver is present in large quantity, Mr. Makin 
believes that the solvent action of nitrous acid is restrained 
by electrical action, the gold becoming the negative and 
the silver the positive pole of a circuit; but as the silver is 
removed, the solution of the gold goes on more rapidly. 
The cause of the evolution of nitrous acid is evident as long 
as there is any silver present, and it often results from the 
use of charcoal to prevent 6 bumping.’ When charcoal 
is thoroughly carbonised, it does not materially affect the 
acid ; but if it contain woody matter, nitrous acid is sure to 
be set free. Mr. Makin has given up the use of charcoal on 
this account. 

The commercial importance of this subject will be ad¬ 
mitted, when we remember the enormous value of the 
metals dealt with in this country, and that the question 
of profit and loss in commercial transactions with them are 
almost entirely in the hands of the assayer. A knowledge 
of these facts may also serve to account for some of the 
discrepancies between assayers. 

Argentiferous and Auriferous Ores .—In the assay of 
auriferous ores, the button produced by cupellation com¬ 
monly contains silver. When the proportion of this metal 
surpasses that of inquartation, the button is flattened be¬ 
tween two pieces of paper, and treated by pure nitric acid. 


GIG 


THE ASSAY OF GOLD. 


The gold remains under the form of a yellowish-brown 
powder, which is weighed immediately, or fused in the 
cupel enveloped in a sheet of lead. When the quantity is 
extremely small and imponderable, we can assure ourselves 
at least of its presence by treating the residue left by nitric 
acid with aqua regia ; if it contain gold, it dissolves and 
gives a yellowish liquid, in which a drop of solution of 
chloride of tin or the crystallised chloride forms a deposit of 
purple of Cassius of a violet colour : this character proves 
the presence of the smallest traces of gold. When the 
gold predominates in the button, it is necessary to re-fuse it 
with three times or less its weight of silver, and recommence 
the assay with the addition of this preparation of silver. 

Sea-salt .—We can, according to M. Gay-Lussac, make 
assays of the alloys of gold, silver, and copper with great 
exactitude, by means of the standard solution of sea-salt. 
When the alloy contains live or six times more of silver and 
copper than of gold, a known weight of the alloy is taken, 

containing nearly 1 gramme of silver ; it 
is dissolved in a matrass (fig. 128) capable 
of containing about 200 grammes of water, 
with 4G2 grs. of nitric acid, at 1*26 sp. gr., 
and boiled for ten minutes. The assay is 
finished as usual; but in order to leave 
the gold and separate the silver, super¬ 
saturate the solution with ammonia, which 
dissolves the chloride; wash the residue 
twice in succession with ammonia, then 
place in a crucible to anneal. If the gold 
were alloyed with silver and copper in a larger proportion 
than 1 to G, a known quantity of fine silver should be added, 
and then deducted from the assay. In order to avoid all 
loss, the bottom of the crucible is lined with paper, and the 

alloy placed thereon, and the latter covered with fused 
borax. 



M. J. Nickles, in some remarks on the extraction of 
auriferous silver from its ores, says, that 6 though the treat¬ 
ment of argentiferous ores is easy, and that of auriferous 
ores not very complicated, it is otherwise when the two 



METHOD OP G. ROSE. 


G17 


metals are associated, for then the properties of the one 
prevent the manifestation of the properties of the other. 
If, for instance, auriferous silver is treated by chlorine 
water, the core immediately becomes covered with a 
coating of chloride of silver, which protects the rest from 
the action of the solvent. If this is attacked by salt water, 
ammonia, or hyposulphite of soda, the core becomes un¬ 
manageable, the chloride of silver dissolves, it is true, but 
leaves behind it a layer of metallic gold which in its turn 
resists the action of the solvents of chloride of silver. 

4 After many tentative trials the simple plan occurred to 
the author of. associating the two solvents, chlorine and 
chloride of sodium. He took salt water concentrated and 
saturated with chlorine, and digested the auriferous alloy 
in it. By burning an ore of this kind and then washing it 
with the above solvent, the chlorine attacks the metallic 
particles, and then transforms them into chloride, which is 
dissolved by the sea-salt. 

4 It is thought that this solvent may serve for the treatment 
of ores so poor in metals as to be discarded for the ordinary 
extracting processes.’ 

Aqua Ilec/ia .—When gold is the largest portion of the 
alloy, and when there are reasons for not adding silver, the 
parting can be made by aqua regia. In this case, all the 
gold is dissolved, and the silver converted into chloride; 
the chloride is washed, dried perfectly, and weighed. 
When the gold is precipitated by proto-sulphate ol iron, it 
is washed with a little muriatic acid, and annealed strongly 
before weighing or even carrying the annealing so far as to 
fuse it, and then cupelling it with lead. 

If an alloy, containing much silver, be treated by this 
process, it sometimes happens that the excess ol chloride ol 
silver prevents the complete solution of the gold. In this 
case it is necessary to reduce the alloy to an excessively thin 
plate, to dissolve the chloride in ammonia, and to treat atresh 
with aqua regia. This process can rarely be made use of 
in the large scale, because the precipitation of gold by 
sulphate of iron is long and troublesome. 

Method of M. Rose.— M. G. Rose fuses the alloy with 


G18 


THE ASSAY OF GOLD. 


lead, over a spirit-lamp, in a porcelain crucible, acts on 
it with nitric acid, which dissolves the silver and lead, 
precipitates the silver by a solution of chloride of lead ; 
lastly, the auriferous residue is dissolved by aqua regia , 
and the gold precipitated by protochloride of iron. 

Standard of the Alloys of Gold. —The real standard of the 
alloys of gold is expressed in fractions of unity, as in the 
case of alloys of silver. We suppose 24 carats in unity, and 
32-32nds in the carat; the unity contains then 768-32nds. 
After these data the following table has been formed, 
which expresses the.relation of 32nds and carats to decimal 
* fractions of the unity. 


32nda 




Decimals 

Carats 




Decimals 

1 



• 

0001302 

1 



0 

004 L067 

2 



« 

0-002604 

2 



« 

0083334 

3 



• 

0-003906 

3 



0 

0-125001 

4 



• 

0-005208 

4 



0 

0-166667 

5 



• 

0-006510 

5 



0 

0-208333 

6 



• 

0007912 

6 



0 

0-250000 

7 



• 

0009115 

7 



0 

0-291666 

8 



• 

0010415 

8 



0 

0-333333 

9 



• 

0011718 

9 



0 

0-374999 

10 



• 

0013021 

10 



0 

0-416667 

11 



• 

0-014323 

11 



0 

0-458630 

12 



• 

0015625 

12 



0 

0-500000 

13 



• 

0-016927 

13 



0 

0-541667 

14 



t 

0018230 

14 



0 

0-583333 

15 



0 

0019531 

15 



0 

0 624555 

16 



0 

0020833 

16 



0 

0-666667 

17 



0 

0 022135 

17 



0 

0-707333 

18 



0 

0-023436 

18 



0 

0-750000 

19 



'• 

0024740 

19 



0 

0-791666 

20 



0 

0026042 

20 



0 

0-833333 

2L 



0 

0027343 

21 



0 

0-874999 

22 



0 

0-028614 

22 



0 

0-916666 

23 



0 

0-029948 

23 



0 

0-958333 

24 



0 

0-031250 

24 



0 

1-000000 

25 



0 

0032552 






26 



0 

0033854 






27 



• 

0035156 






28 



0 

0036460 






29 



0 

0037760 






30 



0 

0039062 






31 



0 

0040364 






32 



0 

0-041667 







Assay of the Alloys of Gold and Copper , or Gold , 

Silver , and Copper. 

Preliminary Assay. —As in the case of silver assaying 
the quantity of lead to be employed is of importance, a 









ASSAY OF ALLOYS (ASSAY PROPER). 61‘J 

preliminary assay must be made when the standard of the 
alloy to be examined is not approximatively known. It is 
thus effected:—To 2 grains of the alloy add 6 grains of 
fine silver and 50 grains of pure lead. The lead must be 
introduced into a hot cupel, and when fused, and its surface 
fully uncovered, the alloy and silver may be added, wrapped 
either in thin paper or a small quantity of lead foil. The 
cupellation finished, and the cupel cold, the button of gold 
and silver must be removed from the cupel by aid of the 
pliers, and if necessary cleansed. Hammer it to a thin 
plate on the anvil, place it in a small evaporating basin, and 
treat it with half an ounce of nitric acid. (It may be here 
mentioned, that the nitric acid employed in the assay 
of gold must be chemically pure, and special care must be 
taken that it contains no trace of chlorine.) The evapora¬ 
ting basin is gently heated until all action ceases. The 
brownish residue *is repeatedly washed with hot water, 
dried, ignited, and weighed; and from its weight the 
amount of lead and silver to be added in the actual assay 
may be determined. The presence of copper in the alloy 
is indicated by the blackness of the cupel where it is satu¬ 
rated with oxide. 

Assay Proper .—In this case it will be supposed that 
standard gold is the alloy operated on, and that preliminary 
assay has given about 91J> per cent, of gold. On referring 
to the table (page 610), it will be found that between 27 
and 30 parts of lead are required for such a percentage 
of gold, and that, according to the general observations on 
this class of assay, three times its weight (that is, the weight 
of fine silver) will be required to so dilute the gold that 
nitric acid can attack and dissolve out the whole of the 
silver combined with it. 

Place the weight representing 24 carats in the pan of the 
balance, and exactly counterpoise it with the gold to be 
assayed; two portions should be thus weighed. Two 
portions of fine silver must now .be weighed ; 33 grains will 
be required for each 24 carats of gold, as 22 carats, or 11 
grains, of fine gold exist in the 24 carats, and .three times 
the quantity of silver is necessary. 300 grains of lead must 


620 


THE ASSAY OF GOLD. 


be placed in a hot cupel (two being thus prepared), and, as 
in the preliminary assay, when the surface is fully uncovered, 
the gold and silver are added, and the cupellation pro¬ 
ceeded with, taking all the precautions already fully pointed 
out elsewhere. 

The button so obtained is cleansed, hammered on the 
anvil, then annealed and passed between the rollers of a 
small flatting-mill; being occasionally annealed, in order to 
prevent the laminated button cracking at the edges. When 
reduced to the desired degree of thinness it is again an¬ 
nealed, and rolled round a quill or glass rod into a spiral, 
termed a cornet. This cornet is placed in a parting flask 
with 1^ oz. of nitric acid, sp. gr. 1 * 16, very gently heated 
to the boiling-point, and at that maintained for ten minutes. 
The acid is then to be poured off, and 2 oz. of nitric acid, 
sp. gr. 1'26, added, and again boiled for ten minutes. This 
second acid is also poured off, and a third quantity of like 
specific gravity added and boiled. The cornet is then well 
washed with distilled water, and the flask, tilled with dis¬ 
tilled water, is inverted, having its mouth closed with the 
thumb. The cornet will fall through the water without 
breaking, and can be introduced, together with some of the 
water, into a small crucible (cornet crucible), the water 
poured off, the crucible and gold gradually dried, and then 
heated to redness. When cold, the final operation of 
weighing may be performed, thus :—The weight represen¬ 
ting 22 carats is placed in one pan of the balance, and the 
cornet in the other: as the gold employed was supposed to 
be standard, it ought to weigh exactly 22 carats. If, how¬ 
ever, gold of greater or less fineness had been submitted to 


assay—say of 23 and 21 carats respectively—1 carat weight 
would have been required in the pan containing the 22 
carat weight, to counterbalance the gold carat: in this case 
the gold would be 23 carats fine, or, in the usual mode of 
reporting, 4 one carat better.’ If, on the other hand, the 1 
carat weight had been found necessary in the pan containing 
the cornet, the gold would be 21 carats fine, or 6 one 
carat worse/ 

In cases where it is known that the gold under examination 


PARTING ASSAYS. 


6*21 


contains no silver, the only alloy being copper, its fineness can 
be determined by cupelling 24 carats with its proper 
portion of lead, and weighing the resulting button, which 
should represent the amount of fine gold in the alloy 
assayed. 

Parting Assays. — Parting assays are those assays by 
which the amount of fine gold and fine silver in any alloy is 
determined. When the amount of gold exceeds that of the 
silver, it is called c gold parting ; ’ when the amount of silver 
exceeds that of the gold, c silver parting.’ 

In this assay the weights employed in the silver assay are 
employed, as the report is made in ounces of fine metal per 
pound Troy. 

12 grains (representing 1 lb. Troy) of the alloy are 
weighed off, cupelled with 300 grains of lead, and the re¬ 
sulting button, containing only gold and silver, is weighed. 
Suppose it weigh 10 grains, then 2 grains, = 2 ounces in the 
pound of alloy, is copper or some other metal, which has 
been oxidised and carried into the cupel with the litharge. 
A preliminary assay must be made of the alloy, to ascertain 
the approximative quantity of silver and gold, so as to 
apportion the amount of silver in the assay proper: this 
amount being found, it is to be weighed off, added to the 
button of fine gold and silver obtained as above, and the 
whole cupelled with 200 grains of lead; the cupelled mass 
of gold and silver laminated and treated with nitric acid, as 
already described, and the resulting gold weighed. Suppose 
the weight to be 8 grains, = 8 ounces, the result would stand 
thus:— 

Copper or other base metal . . . 2 oz. 

G old. . ...... 8 ,, 

Silver . . . . ' . . 2 „ 

12 oz. 

The above arrangement is very convenient for accomplishing 
gold assays, and is the one employed in the assay office of 
the French Mint. The annexed cut (fig. 129) represents this 
apparatus. 

The assay flask, M, being charged with the cornet, a 
constant amount of acid is added with a pipette. On the 
addition of the second acid a small piece of charcoal is 


622 


THE ASSAY OF GOLD. 


placed in the flask : this serves to prevent bumping during 
ebullition. The flasks are supported on a plate of sheet 


Fig. 129. 



iron, P, pierced with holes, or by a grating, and the acid va¬ 
pours, before escaping by the flue, pass into glass tubes, T T , 
about half an inch in diameter, and four feet long : at each 
end a narrower tube, t , is fused. The lower tube freely 
enters the neck of the flask ; and as the space between is so 
small that a layer of acid remains suspended and obstructs 
the passage of the acid vapours, they are thus forced to pass 
into the large tube, where, for the greater part, they con¬ 
dense and fall into the flasks. By this means the quantity 
of acid employed in the assay can be diminished, as there is 
no loss by evaporation, and the results are found to be more 
constant. In order that the passage to the large tube for 
the acid vapours may always remain free, the end of the 
























BLOWPIPE REACTIONS OF GOLD. 


C23 


narrow tube passing into the flask must be cut at an angle 
(see P). The drops of acid collect at this part, and never 
close the tube. 

For the assay of gold and silver alloys by Gay-Lussac’s 
normal solution, see page 616. 

Assay of Tellurides and other native mineralised substances 
containing Gold .— These assays are made in the scorifier 
in precisely the same manner as for silver substances of a like 
kind. The button resulting from cupellation is treated byquar- 
tation if necessary, and by nitric acid, as already described. 

BLOWPIPE REACTIONS OF GOLD. 

The blowpipe reactions of gold are :— 

Graphic Gold.— On charcoal , fuses into a dull grey me¬ 
tallic bead, covering the charcoal with a white smoke, which 
disappears with a green or bluish light, when the reducing 
flame is thrown upon it. After a continued blast, a bright 
yellow metallic grain is obtained. It is, after cooling, bril¬ 
liant and malleable. 

In the open tube it deposits a smoke, which is white, 
excepting in the neighbourhood of the assay, where it is 
greyish. This is sublimed tellurium. This deposit forms 
limpid drops when the flame is directed upon it. 

Telluriferous and Plumbiferous Gold. — Alone , on charcoal 
it fuses like the preceding, and forms a pulverulent deposit 
on the support; but this deposit is yellow ; it disappears in 
the reducing flame with a blue colour, which is not at all 
green. It gives, after a strong blast, a grain of gold, which 
ignites at the instant of congelation. This grain is malleable. 

In the tube it fumes, giving a very sensible fume of sul¬ 
phurous acid. It then gives a sublimate, which is grey close 
to the assay, but white elsewhere. 


624 


THE ASSAY OF PLATINUM. 


CHAPTEE XVII. 

TIIE ASSAY OF PLATINUM. 

Platinum is found in a native or metallic state. It occurs 
very rarely, yet it is exceedingly probable that wherever 
gold is found this metal will more or less accompany it. 

It is found disseminated in sand, in the form of grains 
varying in size from gunpowder to hempseed: this last size 
they rarely exceed ; yet, as in the case of gold, nuggets 
have been found of large size and weight. Its colour is 
steel grey, or rather, a tinge between silver white and steel 
grey. 

The sands from which Platinum is derived are remarkable, 
from the number and importance of their principal con¬ 
stituents. With the platinum may be found Au, Ag, Ilg, 
Fe, Cu, Cr, Ti, Ir, Os, R, and Pd. Besides all these 
metals, precious stones have also been found associated 
with it. 

Analysis of Platinum Ores .—The following is the method 
proposed by Berzelius. The operator first separates mecha¬ 
nically the particles of ore which differ in appearance. All 
those which are attractable by the magnet are next removed. 
Independently of the spangles of metallic iron which were 
first detected by Osann, the platinum sands often contain 
metallic compounds of iron and platinum, not only capable 
of being attracted by the magnet, but possessed even of 
polarity. These grains have a different composition from 
those not magnetic, as shown in the two following analyses by 
Berzelius. 


Berzelius’s assay by aqua regia. 


625 


Analysis of the non-magnetic grains :— 


Platinum . 





78-94 

Iridium 

Rhodium . 





4-97 

•86 

Palladium . 





•28 

Iron . 





11-04 

Copper 





•70 

Osmide of iridium 

of the magnetic 

[ in grains 
[_ in scales 

grains 




1-00 

•96 

98-75 

Platinum . 





73-58 

Iridium 





2-35 

Rhodium . 





1-15 

Palladium . 





•30 

Iron . 





12-98 

Copper 





5-20 

Insoluble matters 





2-30 

97-86 


These grains being separated, their relative proportion is 
estimated. 

The ore is to be treated with diluted hydrochloric acid.* 
The object of this is to free it from the coating of peroxide 
of iron with which it is often covered, and to dissolve the 
metallic iron. The quantity of iron separated from the ore 
in this manner is to be estimated. 

The ore must not be ignited until it has previously been 
weighed ; for during the ignition it generally acquires a 
coating of peroxide of iron, and a consequent increase of 
weight. It is sufficient to dry it upon a hot sand-bath. 

The operator must not employ too large a quantity of the 
ore for analysis. Berzelius thinks about 30 grains is the 
best quantity. Sometimes, however, when the object is to 
determine with great accuracy the quantity of a constituent 
which occurs, but in a very small relative proportion, a 
larger quantity of the ore must be dissolved; but, in such a 
case, every other constituent is to be neglected. 

Berzelius determines the solution of the weighed metal by 


* At the mint in St. Petersburg they treat the ore with aqua regia ; they 
use 10-15 parts of the latter, consisting of 3 parts muriatic acid of 1*18 spec, 
gravity and one part nitric acid of P04 spec, gravity, for one part of ore. The 
ore is digested in porcelain vessels for 8-10 hours, when it will be found to be 
dissolved. 


















62« 


TIIE ASSAY OF PLATINUM. 


aqua regia , in a glass retort furnished with a receiver, which 
is kept constantly cool. The acid distilled over during the 
solution is yellow, which colour does not proceed merely 
from the presence of chlorine, but from the constituents of 
the solution which are carried over mechanically. 

The acid is distilled until the liquid has a syrupy con¬ 
sistence, and congeals on cooling. The saline mass so. 
ormed is dissolved in the smallest possible quantity of 
water, and the solution is poured off with ail due precaution. 
The acid distilled over into the receiver is poured upon the 
undissolved portion of the ore in the retort, and again 
distilled. The second distillation generally effects the com¬ 
plete solution of the platiniferous matter. 

If the distilled liquor be not colourless it must be re¬ 
turned into the retort and redistilled. The residue must be 
evaporated to a syrupy consistence as before, and treated 
with water. The distilled liquid generally contain a small 
portion of peroxide of osmium, of which a part is lost by 
the redistillation ; its quantity, however, is in general very 
small. 

The colourless distilled liquid is diluted with water, and 
saturated either with ammonia or with hydrate of lime. 
The acid, however, must remain a little in excess. The 
object of this saturation is to prevent the decomposition of 
the sulphuretted hydrogen gas, with which the solution is 
afterwards to be precipitated. 

The precipitation is to be made in a flask which can be 
closely stoppered, and of such a size as to be nearly filled 
with the solution. When the solution contains free hydro- 
sulphuric acid, the flask is closed, and left to itself until it 
is perfectly bright, which will be in about two days. The 
clear liquid is removed by a pipette, and the. sulphide of 
osmium collected in a weighed filter, in which it is washed, 
dried, and weighed. According to theory, the resulting 
sulphide of osmium should contain 60’6 per cent, of that 
metal; but it is not obtained free either from moisture 
or excess of sulphur : it is also slightly oxidised during 
the process of drying. According to some experiments 
made by Berzelius with weighed quantities of this sub- 


Berzelius’s assay by aqua regia. 


627 


stance, it appears that the sulphide of osmium obtained 
by the operation just described contains from 50 to 52 per 
cent, of osmium. In general, however, the quantity of 
osmium is so small, that an error of a few hundredths in 
the reckoning of the quantity of osmium contained in this 
preparation is of no importance in regard to the analysis. 

Respecting the metallic solution from the retort, it some¬ 
times happens that after the saline mass has been dissolved 
in water, it smells slightly of chlorine. 

This happens through the decomposition of a portion of 
the chloride of palladium. The solution must be allowed to 
digest until it no longer smells of chlorine. If the solution 
became troubled during the digestion, a portion of oxide of 
palladium is precipitated, which must be redissolved. The 
solution is filtered through a weighed filter, upon which is 
collected that portion which is undissolved. This portion 
consists of grains of osmide of iridium, of spangles of the 
same alloy, and of grains of sand, which could not be sepa¬ 
rated mechanically before the analysis. Sometimes, in ad¬ 
dition to these, a black powder is found, which has the 
appearance of charcoal, and capable of passing through the 
filter during the washing of the other grains. This is per¬ 
oxide of iridium, and is due to the presence of too much 
nitric acid in the aqua regia. As this occasions much extra 
work in the analysis, an excess of hydrochloric acid must be 
employed in making the aqua regia. 

The filtered solution is now mixed with twice its bulk of 
alcohol, specific gravity *833 ; so that the mixture may con¬ 
tain about 60 per cent, of its volume of alcohol. A very 
concentrated solution of chloride of potassium is now added, 
as long as it determines any precipitate. 

The precipitate consists of the double chlorides of potas¬ 
sium and platinum, and of potassium and iridium, contami¬ 
nated with rhodium and a little palladium. 

The precipitate has a fine lemon-yellow colour when it is 
free from iridium ; but when iridium is present it presents 
all shades, from deep yellow to cinnabar-red. 

It is placed upon a filter, and washed with a mixture of 
alcohol (containing about 60 per cent, of anhydrous alcohol) 

s s 2 


628 


TIIE ASSAY OF PLATINUM. 


and a small proportion of concentrated solution of chloride 
of potassium. The precipitate must be washed until the 
liquid passing through gives no precipitate with sulphuretted 
liyd rogen. 

The analysis is now divided into two distinct parts—the 
examination of the washed precipitate A, and treatment of 
the alcoholic liquid B. 

A. The washed salt is dried, and carefully mixed with an 
equal weight of carbonate of soda. The filter, with that 
portion of the precipitate which it is impossible to separate 
from it, must be burnt, and the ashes mixed with a little 
carbonate of soda, and added to that mixed before. The 
whole is very gently heated in a porcelain crucible, until the 
mass is black throughout. 

By acting thus the double salts are decomposed, and the 
platinum, whose oxygen passes awa}- with the carbonic acid, 
is reduced. The rhodium and iridium meanwhile become 
oxidised, and remain in such a state as to permit of their 
separation from the platinum by solution. 

When, instead of following the process just recommended, 
the precipitation of the double salts is effected by muriate of 
ammonia, the heating of the precipitate in a crucible not 
only reduces the platinum, but the rhodium and iridium 
also ; so that, on treating the heated mass with aqua regia , all 
three are dissolved. 

The heated saline mass is washed with water until the 
greater mass of the saline contents is dissolved; diluted hy¬ 
drochloric acid is then added to the remainder to extract 
the alkali, combined with the oxides of iridium and rhodium. 
The mass is washed, dried, and ignited. The fdter may be 
burnt, and an allowance made for the weight of the ashes ; 
but it is to be noted that the filter must be burnt by itself 
lest the metallic oxides be reduced. The mass is afterwards 
weighed. 

When this is done the mass is mixed with five or six times 
its weight of bisulphate of potash, and fused in a platinum 
crucible. During the ignition the rhodium dissolves, and its 
solution is accompanied by an evolution of sulphurous acid 
gas. The platinum crucible must be kept closed during the 


BERZELIUS’S ASSAY BY AQUA REGIA. 


629 


ignition, by a cover which fits well, to check the too rapid 
volatilisation of the acid. As soon as the saline mass 
becomes fixed and crystalline at the surface when the cover 
is removed, the crucible must be taken from the fire and 
cooled. The salt is then dissolved in boiling water, and the 
undissolved residue is treated again with bisulphate of 
potash. The melted salt is red and transparent when it 
contains but little rhodium, but appears dark and black 
when it is nearly saturated with the metal. So long as the 
salt continues to become coloured, the re-melting must be 
repeated. 

In order to avoid in analysis the employment of too large 
a quantity of bisulphate of potash, the operator may supply 
sulphuric acid as follows. When the bisulphate of potash 
appears to have lost the greater part of its free acid, weighed 
portions of the distilled sulphuric acid may be added to the 
mixture, the whole cautiously heated until the water of the 
acid be expelled, and the fusion thereupon be continued. 

The quantity of rhodium can be determined by two 
methods. According to the first, the undissolved platinum 
is washed, ignited, and weighed, and the quantity dissolved 
is equal to the peroxide of rhodium, which contains 71 per 
cent, of metal; or the washings which contain the rhodium 
are super-saturated with carbonate of soda, evaporated to 
dryness, and ignited in a platinum capsule. If the mass be 
now acted on by water, peroxide of rhodium will remain. 
It may be collected in a filter, washed, dried, ignited, and 
finally reduced by means of hydrogen gas. The resulting 
metal is weighed. The rhodium thus obtained sometimes 
contains palladium. This is extracted by aqua regia. The 
solution of palladium is then neutralised and precipitated by 
cyanide of mercury : the precipitate is to be washed, dried, 
and ignited. The residual mass is metallic palladium, which 
may be weighed. 

After the separation of the rhodium, the metallic mass is 
treated with very weak aqua regia , by digestion with which 
pure platinum is dissolved. The solution has a very deep 
colour, which is owing to the peroxide of iridium in supen- 
sion : but when it has become bright by deposition it has a 


THE ASSAY OF PLATINUM. 


630 

pure yellow colour. It is then decanted, and concentrated 
aqua regia , mixed with chloride of sodium, poured upon the 
residue. The solution is now evaporated to dryness. The 
addition of the chloride of sodium is to hinder the pro¬ 
duction of proto-chloride of platinum. A small quantity of 
iridium is dissolved in the very concentrated acid; but, if it 
were not used, a considerable portion of platinum would 
remain mixed with the iridium. 

When the dry mass is acted on by water, peroxide of 
iridium remains unacted upon. If it were washed with pure 
water to dissolve out all the platinum, it would be carried 
through the pores of the filter ; to prevent which a dilute 
solution of chloride of sodium must be employed; and to 
remove the least traces of that, solution of muriate of am¬ 
monia is used. The filter is now to be burnt, and the 
peroxide of iridium remaining, with its ashes, reduced to the 
metallic state by a current of hydrogen gas, and weighed. 

The solution of chloride of sodium containing a small 
quantity of iridium is mixed with carbonate of soda, dried, 
and ignited. The product, freed from soda salts by water, 
and from platinum by weak aqua regia , leaves peroxide of 
iridium, which must be reduced to the metallic state, and 
added to that already obtained. 

In order to arrive at the weight of platinum, the operator 
must deduct the weight of the peroxide of rhodium from 
the united weights of the peroxide of rhodium, peroxide of 
iridium, and platinum. He must then add to the weight 
of the iridium obtained 12 per cent, of the weight of that 
metal, to produce the weight of peroxide of iridium which 
must be deducted from the weight of the platinum. 

The reduction of the platinum from its solution would 
only increase the length of the operation, without adding 
anything to its accuracy. 

B. 7 7 eat merit of the Alcoholic Solution .—This solution is 
poured into a flask capable of being well stoppered, and 
sulphuretted hydrogen passed in to* saturation. It is then 
closed, and allowed to remain at rest for twelve hours in a 
warm place ; at the end of which time all its metallic sul¬ 
phides will be precipitated. Sometimes the solution is red, 


BERZELIUS’S ASSAY WITH AQUA REGIA. 631 

owing either to the presence of rhodium or sesquichloride of 
iridium. 

The solution must now be filtered and evaporated to 
expel all alcohol, during which operation a little more 
metallic sulphide will be precipitated, and which must be 
added to that already obtained. The mixture of sulphides 
thus obtained, consists of the sulphides of iridium, rhodium, 
palladium, and copper; while the filtered solution contains 
iron, rhodium, iridium, and a trace of manganese. During 
the evaporation of the alcohol a greasy-like metallic sul¬ 
phide of a disagreeable odour is deposited, which cannot 
be washed out. After the solution has been entirely washed 
away from this substance, it can be dissolved by pouring a 
little caustic ammonia into the capsule. The solution is now 
poured into a platinum crucible, and evaporated to dryness. 
The moist metallic sulphides are then placed in also, and 
roasted until all sulphurous acid is expelled. On the cessa¬ 
tion of roasting, concentrated hydrochloric acid is poured 
over the mass ; this, owing to the solution of subsulphate 
of copper and palladium, is coloured green or yellowish - 
green. Oxide of iridium and rhodium, with a little platinum, 
remain unacted upon. 

The solution in hydrochloric acid is mixed with chloride 
of potassium and nitric acid, and evaporated nearly to 
dryness ; a dark saline mass is the result, which is com¬ 
posed of chloride of potassium and cupreo-chloride of po¬ 
tassium, with palladio-chloride of potassium. The two first 
of these salts are dissolved out in alcohol, specific gravity 
*833, and the palladium salt is placed on a filter and washed 
with alcohol of the same specific gravity. It contains 28*84 
per cent, of palladium when dried and ignited. 

The spirituous solution, which contains the copper salt, is 
evaporated to get rid of alcohol; and the contained copper 
is precipitated, either by means of pure potash, or by adding 
sulphuric acid and a plate of zinc. 

That portion of the rpasted sulphides which was insoluble 
in hydrochloric acid is fused with bisulphate of potash until 
it ceases to become coloured. The mixture, in this case, 
contains much more rhodium than the precipitate obtained 


632 


THE ASSAY OF PLATINUM. 


at the commencement of the analysis. The residue undis¬ 
solved by bisulpliate of potash, which is peroxide of iridium 
with a little platinum, is treated with aqua regia , and the 
peroxide reduced by hydrogen gas, as stated in a former 
part of the analysis. 

The concentrated solution from which the sulphides were 
precipitated contains only iron in a state of protochloride, 
with a small quantity of iridium and rhodium, and a trace 
of manganese. It must be mixed with a proper quantity of 
nitric acid, and boiled till the iron is fully oxidised. The 
peroxide of iron is then precipitated by caustic ammonia, 
and the precipitate washed, ignited, and weighed. 

This peroxide of iron, however, contains a small quantity 
of iridium and rhodium, to separate which, after weighing 
the peroxide, it must be reduced by hydrogen gas. The 
reduced metal is treated with hydrochloric acid to dissolve 
iron, and the black undissolved portion is collected on a 
filter, ignited with exposure to air, and weighed ; its weight 
deducted from that of the peroxide of iron, previously ob¬ 
tained, leaves the quantity of the latter in a pure state. The 
solution, filtered from the precipitate by ammonia, is mixed 
with carbonate of soda in sufficient quantity to decompose 
the ammoniacal salts, and evaporated to dryness. On treat¬ 
ing the residue with water, after a gentle ignition, peroxides 
of iridium and rhodium remain undissolved ; but they are 
generally too small for separation. 

The following plan will serve to detect platinum in ad¬ 
mixture with gold and other heavy matters obtained by 
washing or vanning sands, earths, &c.:— 

Act on a small quantity by mercury, and separate the 
amalgam: by this means the gold is removed. To the 
residue add aqua regia , and boil; evaporate the solution to 
dryness ; add a little muriatic acid and water ; boil and 
filter. To the filtered solution add a strong solution of sal 
ammoniac (chloride of ammonium). If a bright yellow, or 
reddish-yellow, granular precipitate falls, platinum is present 
in the sand. 

A still more ready method is the following : Separate as 
much earthy matter as possible by careful washing. If gold 


DEVILLE AND DEBRAY’S METHOD. 


633 


is present, separate that by amalgamation. Dry the residue, 
and take its specific gravity: if it be above 10, platinum is 
most likely present. The specific gravity of native platinum, 
free from earthy matter, is from 16 to 19. 

The following method of Analysis of Platinum Ores, by 
MM. Deville and H. Debray, is of interest. The ores of 
platinum contain the following substances:— 

1. Sand. The whole of the sand is never removed by 
washing the ore ; and the sand contains quartz, zirconium, 
chromate of iron, and, in the Eussian ores, titanate of iron. 

2. Osmide of iridium. 

3. Platinum, iridium, rhodium, and palladium, combined, 
no doubt, in the form of an alloy. 

4. Copper and iron, which exist in the ores in a metallic 
state, for the iron found in the sand is not soluble in acids. 

5. Gold, and, oftener than is supposed, a little silver. 
The latter metal is generally found with the palladium, and 
it is very rarely that palladium is obtained quite free from 
silver when it is prepared by the old processes. 

1. Sand .—To estimate the sand we take a small assay 
crucible, or an ordinary crucible with smooth sides, and 
melt in it a little borax, so as to glaze the inside. We now 
introduce from 7 to 10 grammes of pure granulated silver, 
and 2 grammes of the ore fairly taken and weighed very 
accurately. Over the platinum we put 10 grammes of fused 
borax, and oue or two small pieces of wood charcoal. The 
silver is now melted, and care must be taken to keep it for 
some time a little hotter than the melting point, so that the 
borax may be very liquid, and may dissolve the vitreous 
matters which accompany the platinum and constitute the 
sand. The crucible is now allowed to cool, and when it is 
cold, the button, which will contain the silver, osmium, 
platinum, and all the other metals, is detached, and if 
necessary digested for a time with weak fluoric acid to 
remove the last portions of borax. It is now heated to a 
faint redness, and then weighed. The weight of the button, 
subtracted from the sum of the weight of the ore and silver 
employed, will give the amount of sand contained in the ore. 
For example :— 


G.34 


TIIR ASSAY OF PLATINUM. 


Milligr. 

Californian ore.. 2000 

Silver. ....... 7221 

9221 

After fusion, the button weighed . . 91(32 

Consequently, the ore contained, sand. . 59 

It is very important to know this number, for it represents 
the only matter absolutely destitute of value which the ore 
contains ; and this simple operation may be considered the 
most important performed in estimating the value of an ore. 
It is, besides, performed so quickly that it is as well to do 
at the same time two or three specimens, taken from differ¬ 
ent parts of a lot of platinum powder. 

2. Osmide of Iridium. —Another 2 grammes of the ore 
weighed very accurately are treated with aqua regia at 70° 
(Cent.) until the platinum is entirely dissolved. The aqua 
regia must be renewed occasionally for 12 or 15 hours, or 
until it is no longer coloured. It is best to perform this 
operation in a large beaker, and to place a cover over it 
to prevent loss. The solution must be decanted with the 
greatest care from the metallic spangles of the osmide of 
iridium and the sand which remain at the bottom of the 
beaker. If necessary it may be filtered, but as little as possible 
of the osmide must be allowed to go on the paper. The 
insoluble residue must be washed by decantation, then dried 
and weighed, after having added what remained on the 
filter. By subtracting the weight of the residue from the 
weight of the sand obtained in the former operation, we 
obtain the weight of the osmide of iridium. For instance, 
in the Californian ore we had :— 

Milligr. 

Osmide of iridium and sand . . . .81 

Sand ........ 59 

Osmide of iridium.22 

The button obtained in determining the sand might be 
employed in this operation. In that case it is necessary to 
dissolve out the silver with nitric acid, and then proceed 
with the residue, as we have just directed. 

3. Platinum and Iridium .—The solution in aqua regia 
obtained in the last operation is evaporated to dryness at a 




DEVILLE AND DEBRAY’S METHOD. 


G35 


low temperature, and the residue is redissolved in a small 
quantity of water (if it should not entirely dissolve in the 
water, some more aqua regia must be added, and the evapo¬ 
ration repeated), to which is added about twice as much 
pure alcohol; lastly, we add a great excess of sal ammoniac 
in crystals. The whole is now slightly warmed to complete 
the solution of the sal ammoniac, it is then stirred, and 
afterwards set aside for 24 hours. The orange-yellow, or 
even reddish-brown precipitate, which is formed contains 
the platinum and the iridium, but some remains in the 
solution. The precipitate must be thrown on a filter and 
washed with alcohol. Afterwards the filter is dried in a 
.platinum crucible, placed, for greater safety, within a larger 
one, and afterwards heated by degrees to low redness. The 
crucibles are now uncovered, and the filter is burnt at the 
lowest possible temperature. Once or twice after the 
incineration of the filter a piece of paper saturated with 
turpentine should be introduced into the crucible, by which 
means the oxide of iridium will be reduced, and the ex¬ 
pulsion of the last traces of osmium will be effected. The 
crucible is now heated to whiteness until it no longer loses 
weight, or the reduction is finished in a current of hydrogen. 

The liquid separated from the platinum-yellow by filtra¬ 
tion, is evaporated until the chloride of ammonium crys¬ 
tallises in great quantity. It is allowed to cool, is then 
decanted, and on a filter is collected a small quantity of a 
deep violet-coloured salt, which is the ammonio-cliloride of 
iridium mixed with a little of the platinum salt. This is 
first washed with a solution of sal ammoniac, and then with 
alcohol. The salt is then ignited, and if necessary reduced 
by hydrogen like the platinum salt. The mixture of 
platinum and iridium obtained by the two reductions is then 
weighed. The two metals are now digested at about 40° 
or 50° (Cent.) in aqua regia, diluted with about 4 or 5 times 
its weight of water—the aqua regia being renewed until it 
is no longer coloured. The residue is pure iridium. To 
obtain the weight of the platinum the weight of the iridium 
is subtracted from that of the mixture of the two. This 
method of separating the two metals is very accurate if 


63 G 


THE ASSAY OF PLATINUM. 


the aqua regia used be weak, and the contact with it pro¬ 
longed. 

4. Palladium , Iron and Copper .—The liquid charged with 
sal ammoniac and alcohol, from which the platinum and 
iridium have been separated, is evaporated to get rid of 
the alcohol, and then treated with an excess of nitric acid, 
which transforms the chloride of ammonium into nitrogen 
and hydrochloric acid. It is now evaporated almost to 
dryness. The residue is removed to a covered porcelain 
crucible which is weighed with great care. When the 
matter is dry it is moistened with concentrated hydro- 
sulphuret of ammonia and afterwards dusted over with 2 or 
3 grammes of pure sulphur. When dry, this crucible is 
placed within a larger one of clay, and surrounded with 
pieces of wood charcoal. The two, covered, are now set in 
a cold furnace which is filled up with charcoal, and the fire 
is lighted at the top to avoid the projection of any matter 
from the crucible, if it were too quickly heated. After 
reaching a bright red heat, the crucibles are allowed to cool. 
The porcelain crucible now contains palladium in a metallic 
state, with the sulphides of iron and copper, and also the 
gold and rhodium. This mixture is moistened with concen¬ 
trated nitric acid, which, after prolonged digestion at 70°, dis¬ 
solves the palladium, iron, and copper, forming at the same 
time a little sulphuric acid. The solution of the nitrates is 
poured off the residue which is washed by decantation, and 
the solutions and washings are evaporated to dryness, and 
then calcined at a strong red heat. In this way the palla¬ 
dium is reduced, and the iron and copper pass to the state 
of oxides, which are easily separated from the palladium 
by means of strong hydrochloric acid. The palladium 
remains in the crucible in which it is again strongly ignited 
and then weighed. 

The chlorides of iron and copper are now evaporated to 
dryness at a temperature but little above 100° (Cent.) and 
are then treated with ammonia. The sesquichloride of iron 
having lost nearly all its acid, has become insoluble; but 
the chloride of copper is readily dissolved, and may be 
filtered from the iron which is washed, ignited, and weighed. 


guyard’s process. 


637 


The copper solution is now evaporated almost to dryness, 
and then mixed with excess of nitric acid, and heated to 
drive off the chloride of ammonium. Afterwards the nitrate 
of copper is ignited and weighed. The weight of the 
copper is always so small that the hygrometric water the 
oxide of copper may absorb may be neglected. 

5. Gold and Platinum .—The residue insoluble in nitric 
acid is weighed and treated with very dilute aqua regia 
which takes up the gold, and sometimes, but very rarely, 
traces of platinum. To ascertain if platinum be present, 
evaporate to dryness, and re-dissolve by alcohol and chloride 
of ammonium. If any platinum-yellow remain, it must be 
ignited and weighed. The difference in the weight of the 
porcelain crucible before and after the treatment by aqua 
regia , gives the weight of the gold, from which, if any be 
found, the weight of the platinum must be deducted. 

6. Rhodium .—The residue left in the crucible is rhodium, 
which must be reduced in a current of hydrogen. 

We append the results of some analyses of platinum ores, 
by MM. Deville and Debray. 


Analyses of Platinum Ores from various sources. 



Columbia 

California 

Oregon 

Spain 

Australia 

Russia 

Platinum . 

8000 

79-85 

51-45 

45-70 

59-80 

77-50 

Iridium 

1-55 

4-20 

0-40 

0-95 

2-20 

1-45 

Rhodium . 

2-50 

0-65 

0-65 

2-65 

1-50 

2-80 

Palladium . 

1-00 

1-95 

0-15 

0-85 

1-50 

0-85 

Gold . 

1-50 

0-55 

0-85 

3-15 

2-40 

o 

Copper 

0-65 

0-75 

2-15 

1-05 

1-10 

2-15 

Iron . 

7-20 

4-95 

4-30 

6-80 

4-30 

9-60 

Osmide of iridium 

1-40 

4-95 

37-30 

2-85 

25-00 

2-35 

Sand . 

4-35 

2-60 

3-00 

35-95 

1-20 

100 

Osmium and loss. 

• • 

0-05 

• • 

005 

0-80 

2-30 


100-15 

100-00 

100-25 

100-00 

100-00 

100-00 


M. A. Guyard gives the following process for the extrac¬ 
tion of metals from platiniferous residues. 

‘ This process comprises three different operations, which 
I will succinctly describe. 

c 1. Solution of the Residues .—The mother liquors which 
remain after the precipitation of platinum by sal ammoniac 

* Gold, if any, counted in the loss. 
























638 


THE ASSAY OP PLATINUM. 


come from solutions of crude or commercial platinum. 
They always contain iron, mostly produced from the sulphate 
of iron used for the precipitation of gold, lead, copper, pal¬ 
ladium, platinum, and especially rhodium. These mother 
liquors are acidulated by hydrochloric acid, and are then 
ready to be investigated. To recall their composition, I 
shall distinguish them here only as residues in solution. It 
need only be mentioned that iron, which is generally used 
for the precipitation, must be avoided. 

‘ Solid residues are melted at once with three times their 
weight of a mixture of equal parts of soda and nitrate of 
soda. The fusion is effected at a bright red heat in a thick 
iron vessel. It is accomplished without bubbling or pro¬ 
jection, and requires about an hour. During the last twenty 
minutes the mass must be constantly stirred with an iron 
spoon. The operation is extremely simple. 

‘These residues contain osmide of iridium, unattackable 
by all chemical agents, attackable osmide, some grains of 
triple alloy of platinum, iridium, and rhodium, which aqua 
regia will not dissolve, but which nitre completely oxidises 
and completely breaks up. They also contain the gangue 
characteristic of platinum ores—quartz, silicates of all bases, 
titanates, hyacinths, &c. &c. 

‘ The mixture I make use of oxidises all that is oxidisable, 
and breaks up the gangue, which it partly dissolves. The 
melted mass contains all the bodies above mentioned, 
besides a large quantity of oxide of iron, taken from the 
sides of the vessel in which the operation is performed. 
The fused mass is poured into cast-iron moulds. When solid 
it is broken into fragments and boiled with sufficient water 
to obtain a strong solution of soda, capable of holding all 
the gelatinous acids in solution. It also contains osmium in 
the state of osmiate * It is filtered from insoluble matter, 
and then supersaturated with hydrochloric acid. The in¬ 
soluble oxides are freed by washing from the excess of alkali 
and are then dissolved in aqua regia . 

‘ This solution contains iron, copperhead, iridium, rhodium, 

* This solution is separately precipitated by hydrosulphuric acid. Sulphide 
of osmium is thus isolated. 


guyard’s process. 


639 


platinum, and ruthenium. It is separated from the undis¬ 
solved osmide, evaporated to expel the excess of aqua regia , 
and dissolved in water and hydrochloric acid. 

4 2. Precipitation of Liquids by Sulphuretted Hydrogen.— 
Liquids obtained as above are ready for precipitation by 
hydrosulphuric acid. 

4 The apparatus in which all the liquids are precipitated is 
composed of a sulphuretted hydrogen gas generator by the 
action of sulphuric acid on sulphide of iron. This gene¬ 
rator communicates with four or five large earthenware jars, 
holding about 70 litres, arranged precisely as in Wolff’s 
apparatus. A special tube conducts to each of them the 
vapour destined to heat the liquid which they contain. 

4 The whole apparatus is enclosed in a well-fitted wood 
stove placed near a chimney, with which it communicates. 
As to the small quantities of unabsorbed gas, they are con¬ 
ducted into the chimney, where the fire creates a strong 
draught. By this means, also, all smell is avoided during 
the precipitation ; but after the operation air is forced 
through the apparatus from large gasometers. It expels the 
hydrochloric acid which saturates the mother waters, and 
these can then be manipulated free from smell A 

4 The experiment is carried on during the precipitation in 
the following manner : when the generator begins to dis¬ 
engage gas, the temperature of the liquids is raised to about 
70°. This temperature is maintained for nearly fifteen hours, 
that being the time required for the complete precipitation 
of the sulphides, which collect better under the influence of 
heat. The operation is concluded when there remains but 
a very slight yellow tint in the mother liquor, arising from 
the presence of a little soluble sulphide of iridium. This 
mother liquor is poured from the precipitated sulphides into 
a vessel with pieces of iron, which takes off a little of the 
iridium. The sulphides are filtered through linen filters. 

4 3. Purification and Treatment of the Sulphides. —The 
mass of sulphides thus separated from the iron and from 
all other bodies not precipitated by the sulphuretted gas, 

* A carbonic acid generator may be substituted for the gasometers and the 
air with no difference in the result. 


640 


TIIE ASSAY OF PLATINUM. 


contains, in addition to the sulphides of the platinum 
metals, a large proportion of sulphur and the sulphides of 
copper and lead. To get rid of these bodies, I have thought 
of concentrated sulphuric acid, which changes them to 
sulphurous acid and sulphates, while it does not act on the 
sulphides of the precious metals. This refining can be 
effected in an iron vessel, but Mr. Matthey, who neglects 
nothing to ensure the certainty and exactness of the results, 
makes use of platinum. 

4 When, after prolonged boiling, no more sulphurous acid 
is given off, the refining is complete. 

4 The mass of sulphides, diluted with a quantity of water, 
is thrown on filters, and thoroughly washed, until ammonia 
no longer finds any trace of copper or iron in the filtered 
liquid. 

4 At this point precious metals are entirely freed from 
iron, which is so detrimental to them, gfnd from copper, and 
contain only a little sulphate of lead, which separates by 
itself during an ulterior reaction. They are then, moreover, 
in a condition to be dissolved by simple nitric acid or by 
aqua regia , and this is not their least valuable condition. 

4 Treatment of the Sulphides .—The sulphides are next 
dissolved in aqua regia , which should not be previously 
prepared, because its action on sulphates is so sudden and 
energetic; it heats so rapidly, and the disengagement of 
gas is so great that, were it previously prepared, it would 
certainly be thrown from the vessels. 

4 1 add then moderately strong cold nitric acid, and add 
it gradually, because its action is strong. A quantity 
of rutilant vapours are disengaged. Hydrochloric acid is 
added when the effervescence ceases. It is then gradually 
heated to boiling, which is necessary to obtain a complete 
solution. 

‘The solution is poured from the deposited chloride of 
lead, and the ordinary method with sal ammoniac is used 
to separate the different metals it contains. Experiments on 
large quantities of material have fully proved the advantages 
of this process.’ 



C41 


CHAPTER XVIII. 

THE ASSAY OF BISMUTH. 

The following varieties of bismuth ores are met with, but 
are somewhat rare :— 

Oxide of Bismuth. 

Sulphide of Bismuth. 

Persulphide of Bismuth. 

Cupriferous Sulphide of Bismuth. 

Plumbo-cupriferous Sulphide of Bismuth. 

Plumbo-argentiferous Sulphide of Bismuth. 

Lastly, we have Native Bismuth, which, although far 
from common, is the only mineral hitherto found to supply 
the wants of commerce with the pure metal; and the only 
products of it are bismuth slags and cupel bottoms, in which 
oxide of bismuth is present in lieu of oxide of lead ; it some¬ 
times happening that bismuth is employed instead of lead in 
cupellation (see Silver Assay). 

Native Bismuth possesses a tolerably bright metallic 
lustre; its colour yellowish-white, often iridescent. It fuses 
in the candle flame. It is generally found in small amorphous 
lamellar masses, yet it occasionally occurs in acute rliom- 
boidal as well as cubical and octoliedral crystals. 

This substance does not seem to form veins by itself, but 
generally accompanies other minerals, particularly those of 
cobalt, nickel, arsenic, and lead. 

Assay of Native Bismuth. —The assay of native bismuth 
may be done in the same way as that of Antimonium 
crudum, i.e. the bismuth is separated from the gangue in 
which it occurs by heating the mineral in closed vessels, 
as described at the Assay of Antimony. 

Assay of Bismuth Residues, Cupel Bottoms , fc. —These 

T T 


THE ASSAY OF BISMUTH. 


642 

substances must be finely pulverised, and from 200 to 400 
grains mixed with three times its weight of fused borax, 
their own weight of carbonate of soda, and from 100 to 200 
grains of cyanide of potassium, and proceed with all the 
precautions above pointed out. 

In case the mineral contained besides bismuth other 
metals (they are mostly tin, copper, and lead), the resulting 
metal-button will contain part of those metals, and they must 
be determined by the humid process. 

Determination of amount of Bismuth by the Humid 
Process .—Act on 50 grains of the finely powdered substance 
with strong nitric acid until all action ceases, evaporate to 
dryness, add from 50 to 100 drops of strong sulphuric acid, 
well mix with a glass rod, and evaporate to dryness; add 
water, with a few drops of sulphuric acid, and boil. Filter 
the solution, and to the filtered solution add excess of carbo¬ 
nate of ammonia. Collect the oxide of bismuth thus thrown 
down on a filter, wash, and dry; separate it carefully from 
the filter, ignite it, and weigh : every 100 parts correspond 
to 89*87 of bismuth. 

Or the bismuth may be obtained at once in the metallic 
state from the solution prepared as above : by adding to it 
metallic copper in the form of a small sheet, and gently 
heating, the bismuth will separate in the metallic state, and 
can be washed, dried, and weighed, as directed for copper, 
under the Assay of that metal. 

The high price of bismuth for some years past has in¬ 
duced M. Balard to undertake the search for this metal in 
old type metal. When it was cheaper, bismuth entered 
into the composition of the alloy for printing purposes. 

M. Balard proposes to effect this industrial analysis in the 
following way:— 

1. Dissolve the material in nitric acid, so as to transform 
.all the tin into metastannic acid, which isolate by filtration 
from the acid solution of nitrates of lead and bismuth; 
wash with acidulated water, dry, and reduce by charcoal. 

2. Into the liquid, neutralised as much as possible, plunge 
plates of lead, which precipitate all the bismuth in°a 
metallic state ; dry, and melt with a reducing agent 

O tD * 


PREPARATION OF STANDARD SOLUTION. 


643 


3. Precipitate the lead from the last liquid by carbonate 
of soda ; separate, wash, dry, and reduce with charcoal. 

This way of operating gives the three metals in a metallic 
state; it may undergo several modifications for isolating 
the metals under another form according to the arrange- 
ment of the products. To obtain extremely pure subnitrate 
of bismuth, says M. Balard, it is necessary only to neutra¬ 
lise the liquid containing the soluble nitrates, and dilute 
with a large quantity of water naturally free from carbo¬ 
nates, chlorides, or sulphates. After again neutralising and 
diluting with water and repeating the operations several 
times, the greater part of this metal becomes separated in the 
state of white bismuth. 

Mr. R. W. Pearson has given the following process for 
the Assay of Bismuth by weight and by volume. 

Preparation of standard solution .—*7135 grs. of pure 
crystallised bichromate of potash are dissolved in 100 grs. 
of water. Call this solution the biclirome test A. 

In a similar way, prepare a second solution, one-tenth the 
strength of bichrome test A; '07135 grs. of bichromate of 
potash diffused in 100 grs. of water, will furnish such a 
solution; call it the bichrome test B. Biclirome test C, one- 
tenth the strength of solution B, is also prepared by dis¬ 
solving *007135 grs. of the bichromate of potash in 100 grs. 
of water. 

These figures can be multiplied to any convenient number. 
These solutions will contain bichromate of potash, in 100 
grs. of biclirome test A, equal to 1 gr. of bismuth ; in 100 
grs. of biclirome test B, equal to 0T gr. of bismuth ; and in 
100 grs. of biclirome test C, equal to *01 gr. of bismuth. 

The bismuth should be in the form of nitrate, and the 
solution kept hot during the experiment, as the precipitated 
chromate collects more readily than after comple precipita¬ 
tion of the bismuth ; the solution will exhibit a characteristic 
colour, produced by excess of the bichromate of potash. 

By employing a standard solution of bismuth it has been 
ascertained that 71*35 parts of bichromate of potash are 
required to combine with 100 parts of bismuth. 


fi44 


BLOWPIPE REACTIONS OF BISMUTH. 


BLOWFIPE REACTIONS OF BISMUTH. 

Native Bismuth.— Alone , fuses, giving a weak arsenical 
odour. Otherwise, it presents the same phenomena as pure 
bismuth. 

In the open tube it gives a little arsenious acid. Cupelled, 
it tinges the bone ash pure orange-yellow. 

Sulphide op Bismuth. — Alone , in the tube, gives sul¬ 
phurous acid and a white sublimate ; heated to redness, it 
deposits oxide of bismuth round the assay, like pure bismuth. 
On charcoal it fuses with bubbling, throwing out small 
incandescent globules. This agitation lasts but a short time. 

Oxide op Bismuth.— Alone , oxide of bismuth fuses readily 
on the platinum wire, forming a deep brown mass, which 
becomes yellow on cooling. If acted upon by a very 
intense flame, it is reduced, and perforates the platinum. 
It is reduced instantaneously on charcoal. 

With borax it fuses into a colourless glass in the oxidising 
flame. In the reducing flame it becomes greyish, owing to 
the dissemination of particles of bismuth. 

Microcosmic salt forms with it a brownish-yellow glass. 
In the reducing flame, particularly with tin, a glass is formed, 
which is clear and colourless while hot, but becomes greyish- 
black on cooling. Oxide of copper presents nearly the same 
phenomena under the same circumstances, but with this 
difference—that tin produces a red colour. 

Owing to the facility with which bismuth maybe reduced, 
it is nearly always on the metal that the assay is made; 
hence it becomes very important to distinguish it from the 
antimony and tellurium, with which it may be readily con¬ 
founded. 

Firstly, in the matrass neither antimony nor bismuth 
sublime at a temperature the glass can bear. Tellurium, on 
the contrary, gives at once a little smoke (by means of the 
oxygen of the atmosphere), and finally, a grey sublimate of 
metallic tellurium is obtained. 

Secondly, in the open tube antimony gives a white vapour, 
which lines the interior of the tube, and which can be driven 
by heat from one part to another without leaving the least 



BLOWPIPE REACTIONS OF BISMUTH. 


645 


trace. The metallic bead is always covered by a notable 
quantity of fused oxide. 

Tellurium gives much vapour, which attaches itself to the 
sides of the tube as a white powder, which is capable of 
fusion into colourless drops by the application of heat. 

Bismuth gives no smoke if it be not combined with sul¬ 
phur ; and the fused metal is surrounded by the brown fused 
oxide, which strongly attacks the glass. 

Thirdly, on charcoal these three metals give off vapour 
by the action of heat, and leave a ring around the spot on 
which they are placed. That from antimony is quite white ; 
those from bismuth and tellurium, red or orange. If the 
reducing flame be made to play upon them they disappear, 
at the same time colouring the flame a deep green if tellu¬ 
rium be present, and pale bluish-green if antimony. It is 
not coloured at all by bismuth. 


G4G 


TIIE ASSAY OF CHROMIUM. 


CHAPTEE XIX. 


THE ASSAY OF CHROMIUM. 


The principal ore of this metal which occurs in commerce 
is known as chrome iron, or chrome iron ore. It is found in 
amorphous masses of a brownish-black colour, approaching 
an iron grey. Its fracture is uneven, sometimes lamellar; 
and its powder is greyish. 

The two following analyses will give a general idea of its 
composition :— 


Oxide of chromium 
Peroxide of iron . 
Alumina 
Silica . 


. 360 437 

. 370 34-7 

. 21-5 20-3 


5-0 2-0 

99 : 5 100-7 


Assay of Chrome Ore. 


Chrome iron ore, like native oxide of tin, is very difficultly 
decomposable by ordinary re-agents. A good method of 
operating is thus :•—Mix 50 grains of ore, reduced to the 
utmost state of division, with 100 grains of nitrate of potash 
and 200 grains of carbonate of soda; place the mixture in 
a platinum crucible, and expose to a red heat for half an 
hour ; remove the crucible, and allow it to cool. Place it, 
when cold, in an evaporating basin, and add enough water 
to cover the crucible : gradually heat the basin and contents 
to ebullition. The fused mass in the crucible will gradually 
dissolve, and if the operation has been successful there will 
be no undecomposed chrome ore : if, however, there be, it 
must be collected, as in the case of the analysis of tin ore, 
dried again, ignited with nitrate of potash and carbonate 
of soda, and treated with water, as just described. The 
solution which is obtained is deep yellow, its colour being 
due to chromate of potash and soda, which have been 



clarke’s assay of chrome iron ore. 


647 


formed at the expense of the oxygen of the nitric acid, 
which has converted the oxide of chromium into chromic 
acid : thus—- 

Cr 2 0 8 + 30 = Cr0 3 ; 

and the chromic acid so produced combines with potash and 
soda to form the chromates, having the following formula :— 

K0,Cr0 3 +Na0,Cr0 3 . 

The solution is to be filtered from the insoluble residue, 
consisting principally of peroxide of iron, and evaporated to 
dryness with small excess of nitric acid: the dry mass is 
treated with water, and the whole boiled, and, if necessary, 
filtered. It must now be treated with solution of proto- 
nitrate of mercury, which throws down chromate of mercury: 
the proto-nitrate must be added as long as a precipitate is 
produced. The chromate of mercury is collected on a 
filter, well washed, dried, and ignited. During the process 
of ignition the chromate of mercury is decomposed into 
mercury and oxide of chromium of a pure bright green 
colour. 100 parts of this oxide correspond to 70 parts of 
metallic chromium. 

Calvert used for decomposition of chrome iron ore a mix¬ 
ture of 3-4 parts of caustic soda, and 1 part soda-nitre. He 
heated the ore with such mixture for 2 hours in a platinum 
crucible. 

The following process, as described by F. W. Clarke, S.B., 
has given excellent results. 

One part of the finely pulverised mineral is mixed in a 
platinum crucible with three parts of fluoride of sodium, and 
upon the top of this mixture are placed twelve parts of 
bisulphate of potash, which may be either in powder or in 
small lumps. 

Upon heating, the mixture boils up strongly, and after a 
while settles into a clear, tranquil fusion. The boiling is 
chiefly owing to the action of the reagents upon the mineral, 
and not, as might be supposed, merely to the influence of 
the bisulphate upon the fluoride. This is shown by the fact 
that, whenever the reagents are heated together without 
minerals, although some boiling takes place, the addition of 


648 


THE ASSAY OF CHROMIUM. 


a little powdered chrome iron ore fully doubles the violence 
of the action. 

In quantitative analyses it is necessary to keep the crucible 
closely covered, in order to avoid loss from spattering ; and 
to heat carefully, so that the mass may not boil over. The 
bisulphate should never be mixed with the lluoride and 
mineral, because a portion of the assay is then apt to escape 
action, being left on the sides of the crucible by the boiling 
of the mass; but should be placed upon the top of the mix¬ 
ture as above directed, as then the decomposition is complete. 
The mass obtained by this fusion is, in the case of some 
minerals, completely soluble in water. In other cases, basic 
salts are formed, which, although insoluble in water, dissolve 
readily in hydrochloric acid. Almost all of the latter class 
may be rendered soluble in water by the following process: 
The fused mass, after cooling, without removal from the 
crucible, is treated with a small quantity of strong sulphuric 
acid, and again fused. The mass thus obtained is entirely 
soluble in water. There are exceptions to this rule, how¬ 
ever. 

The following results have been obtained. For the sake 
of brevity, we will speak of the fusion with bisulphate and 
fluoride as fusion No. 1, and the subsequent treatment with 
sulphuric acid, as fusion No. 2. 

Fusion No. 1.—Chrome iron ore is decomposed very easily. 
In one case, in which the operation was timed, the fusion was 
complete in less than three minutes from the time the heat¬ 
ing was commenced, and that over an ordinary Bunsen’s gas 
burner. The cooled mass is light green, partly soluble in 
water alone, and entirely soluble in hydrochloric acid. 

Fusion No. 2.—The mass possesses a deeper green colour 
than that obtained by the' first fusion, and a larger propor¬ 
tion of it dissolves in water. In every fusion that I have 
yet made of chromite, however, a small quantity of basic 
salts was formed, requiring treatment with hydrochloric 
acid. 

For the technical determination of chromium in chromite, 
Mr. Clarke says: After fusion with cryolite and bisulphate 
of potash, as previously directed, the mass is to be treated 
with a little strong hydrochloric acid, and allowed to digest 



ASSAY OF CHROMIUM BY STANDARD SOLUTION. 


649 


for about ten minutes. Then upon boiling with water, the 
whole dissolves. The solution should then be neutralised, 
acetate of soda added, and the chromium oxidised to chromic 
acid by a current of chlorine gas, or by boiling with hypo¬ 
chlorite of soda solution. The chromium may then be 
separated from other substances, as directed in Professor 
Gibbs’s paper (‘Am. Journ. Sci.,’ January 1865). When 
chromite is fused with bisulphate of potash and cryolite, and 
saltpetre is added to the mass, as soon as clear fusion is ob¬ 
tained, the chromium is nearly all oxidised to chromic acid. 
If the mass be boiled with a solution of carbonate of soda, 
and the liquid filtered, a filtrate is obtained which contains 
nearly all, but not quite all, the chromium as alkaline chro¬ 
mates, free from iron or alumina; but, invariably, the resi¬ 
due upon the filter contains traces of chromium. When 
chromite is fused with the acid fluoride of potassium, a part 
of the chromium is usually oxidised to chromic acid by the 
oxygen of the air ; and in one case that came under my 
observation, when I came to heat the resulting mass with 
sulphuric acid, red fumes were given off, which were pro¬ 
bably the so-called terfluoride of chromium. 

When bisulphate of potash alone is used for the decom¬ 
position of chromite, &c., it is necessary that the mineral 
should be reduced to extremely fine powder; but when the 
mixture of bisulphate and fluoride is employed, although 
tire mineral should be in fine powder, such an extreme state 
of subdivision is by no means required, and thus much 
labour is saved. 

Determination of Chromium by means of Standard Solu¬ 
tion .—This process is the converse of the determination of 
iron by means of solution of chromate of potash. 

The chrome ore is treated with nitrate of potash and car¬ 
bonate of soda, as above described ; and the solution of 
chromate of potash so obtained has an excess of hydro¬ 
chloric acid added to it. 

It is stated at page 276, under the head of Iron Assay 
by Standard Solution, that 100 parts of metallic iron corre¬ 
spond to and are represented by 88*6 grains of bichromate 
of potash : now 88*6 grains of bichromate of potash contain 
82*96 grains of chromium ; therefore 100 grains of iron arc 


G50 


THE ASSAY OF CHROMIUM. 


equal to 32’96 of chromium. From these data a standard 
solution can be readily made : thus—Dissolve 50 grains of 
harpsichord wire in excess of hydrochloric acid; place the 
solution in the burette, and fill up to 100 on the instrument 
with water, and well mix : it is now evident that every 
division of the burette will equal or represent ’1648 grains 
of chromium. The assay is now thus proceeded with : 
Gradually add the standard solution of iron to the solution 
of chromate of potash (or rather, now, bichromate of potash) 
acidulated with hydrochloric acid, until a drop of the solu¬ 
tion mixed with a drop of solution of ferrocyanide of potas¬ 
sium gives a pale blue colour: a slight excess of protoxide 
of iron is then present, showing that all the chromic acid 
has been reduced to the state of oxide of chromium. Now 
observe how many divisions of the iron solution have been 
required, and multiply them by T648 : the resulting number 
will represent the amount of metallic chromium in the 
sample submitted to assay. 

Blowpipe Reactions of Chromium. 

ORES OF CHROMIUM. 

Chrome Ochre. — Alone , decolourises, and becomes nearly 
white, but does not fuse. 

Borax separates oxide of chromium, and takes a fine 
green colour. 

It dissolves with great difficulty in microcosmic salt, and 
the green colour is not so beautiful as with borax. 

Oxide of Chromium. — Alone , undergoes no change. 

With borax , fuses difficultly, even in small quantity. The 
glass has a splendid emerald-green colour, which is princi¬ 
pally developed during cooling. 

With microcosmic salt it fuses in the exterior as well as 
in the interior flame, furnishing a deep green glass ; and a 
very small quantity of oxide suffices to produce this effect. 

Soda dissolves oxide of chromium on the platinum wire 
in the exterior flame, producing a deep orange glass, which 
becomes yellow on cooling. In the reducing flame it be¬ 
comes opaque. It is green after cooling. 


65] 




CHAPTER XX. 

THE ASSAY OF ARSENIC. 

The minerals from which arsenic is produced are the fol- 

Native arsenic. 

Arsenic kies, FeS 2 -fFeAs, containing 4G,6 As and 19,G S. 

Arsenical kies, Fe 4 As 3 , containing 66,8 As. 

Speiskobalt (Co,Ni,Fe), As. 

Glanzkobalt, CoS 2 -f CoAs. 

Coppernickel, Ni 2 As. 

Nickel and cobalt arsen-kies, (Co,Ni,Fe)S 2 -j-(Co,Ni,Fe)As. 

White nickel-kies, NiAs ; Tennantite (Cu 2 S,SeS) 4 ,AsS 3 . 

Realgar AsS 2 and yellow arsenic AsS 3 . 

Assay for Arsenic .—50 grains of the finely pidverised 
mineral are deflagrated with 200 of nitrate of potash and 
200 of carbonate of soda in a porcelain crucible. When the 
crucible is cold, it and its contents are to be treated with 
Avater, as in the case of chromium. The solution will con¬ 
tain arseniate, and (if the ore had in its constitution sulphur, 
which is most likely) sulphate of potash. Nitrate of lead 
must be added to the solution (made neutral with nitric 
acid, if requisite): a mixture of arseniate and sulphate of 
lead is precipitated : this precipitate is well washed on a 
filter, and digested with dilute nitric acid : this agent dis¬ 
solves out the arseniate of lead, and leaves the sulphate. 
Filter, and saturate the filtered solution with soda, which 
will throw down the arseniate : this must be collected on a 
filter, washed, dried, and weighed. Every 100 parts cor¬ 
respond to 22*2 of metallic arsenic, or 29 parts of arsenious 
acid (the common white arsenic of the shops). 

This method is only approximative : the following is the 
better plan :— 



652 


THE ASSAY OF ARSENIC. 


Digest the ore in strong nitric acid until nothing more is 
taken up (the action may be facilitated by the occasional 
addition of a crystal or two of chlorate of potash), and all 
action on the addition of fresh acid is at an end : dilute 
with water, and filter : to the filtered solution add nitrate of 
lead, and proceed as above. 


653 


CHAPTER XXI. 

THE ASSAY OF MANGANESE. 

The following are the commercially valuable minerals 
containing manganese. 

Pyrolusite, Mn0 2 , containing 18 p.c. of available oxygen. 

Braunite, Mn 2 0 3 „ 10-0 „ „ 

Manganite, Mn 2 0 3 , „ 9 ,, 

Varvicite, Mn0 2 + Mn 0 3 ,H0, „ 13*8 ,, ” 

Hausmannite, Mn0 + Mn 2 0 3 , „ 6*8 „ ,, 

Psilomelane, Mn 2 0 3 . 

Assay of Manganese Ores .—The assay of this metal is 
confined to the amount of peroxide any one of its ores may 
contain. There are several methods of affecting this, and 
the best of these will be described below. 

The following method is described in Graham’s ‘Elements 
of Chemistry,’ page 536 :— 

The value of the oxides of manganese is exactly pro¬ 
portioned to the quantity of chlorine they produce when 
dissolved in hydrochloric acid, and the chlorine can be 
estimated by the quantity of protosulphate of iron it peroxi- 
dises. Of pure peroxide of manganese, 545*9 parts pro¬ 
duce 442*6 parts of chlorine, which peroxidise 3456 parts 
of crystallised protosulphate of iron. Hence 50 grains of 
peroxide of manganese yield chlorine sufficient to peroxidise 
317 grains of protosulphate of iron. 

50 grains of the powdered oxide of manganese to be 
examined are weighed out, and also any known quantity, 
not less than 317 grains, of sulphate of iron. The oxide of 
manganese is thrown into a flask containing H ozs. of strong 
hydrochloric acid, diluted with ^ oz. of water, and a gentle 
heat applied. The sulphate of iron is gradually added in 


G54 DETERMINATION OF TIIE AMOUNT OF PEROXIDES. 

small quantities to the acid, so as to absorb the chlorine as 
it is evolved ; and the addition of that salt continued till the 
liquid, after being heated, gives a blue precipitate with the 
red prussiate of potash, and has no smell of chlorine, which 
are indications that the protosulphate of iron is in excess. 
By weighing what remains of the sulphate of iron, the 
quantity added is ascertained—say m grains. If the whole 
manganese were peroxide, it would require 317 grains of 
sulphate of iron, and that quantity would therefore indicate 
100 per cent, of peroxide in the specimen; but if a portion 
of the manganese only is peroxide, it will consume a pro¬ 
portionally small quantity of the sulphate, which quantity 
will give the proportion of the peroxide, by the proportion 
as 317 : 100 :: m : percentage required. The percentage 
of peroxide of manganese is thus obtained by multiplying 
the number of grains of sulphate of iron peroxidised by 
0*317. It also follows, that the percentage of chlorine 
which the same specimen of manganese would afford, is 
obtained by multiplying the number of grains of sulphate of 
iron peroxidised by 0 2588. 

The quantity of oxygen which any peroxide of manganese 
loses by becoming protoxide, can be arrived at very exactly 
and in a very convenient manner, by heating it, in a finely 
powdered state, with a solution of oxalic acid. The action 
commences even in the cold; a part of the oxalic acid 
is converted into carbonic acid, and an oxalate of the 
protoxide of manganese is formed. Oxalic acid contains 3 
atoms of oxygen to 2 atoms of carbon, since carbonic acid 
contains 4 atoms of oxygen to 2 atoms of carbon : it may be 
seen that the oxygen which is estimated is equal to one-fourth 
of that contained in the carbonic acid. The carbonic acid 
is collected as carbonate of baryta, and the operation per¬ 
formed as follows :— 

Place in a small flask 1 part of the pulverised mineral, 4 
or 5 parts of oxalic acid, and 10 parts of water; adapt 
immediately to the matrass a recurved tube of small 
diameter, placing its open end into a vessel holding about 
half a pint of saturated baryta water, which must be fre¬ 
quently agitated in order to favour the combination of the 


THE ASSAY OP MANGANESE. 


G55 


evolved carbonic acid with the baryta in solution. When 
e lisen & a 0 ement of gas nearly ceases, the contents of the 
flask must be made to boil in order to expel all carbonic 
acid. It sometimes happens that all the peroxide of man¬ 
ganese assayed is not decomposed by the oxalic acid, which 
can be ascertained if it has not changed colour, in which 
case the operation must be repeated. 

The following is a method contrived by Dr. Thompson, 
and is a modification of the one just described. When 
ordinary care is taken, it is nearly as accurate as assays 
made in a more expensive manner and with more trouble¬ 
some apparatus. 


Take 50 grains of the finely powdered mineral, and 
place it in a small flat-bottomed flask (capable of standing 
the heat of a sand-bath), together with about li ozs. of 
water, and a ^ oz. of sulphuric acid. Then place loosely a 
plug of cotton-wool in the neck to absorb any moisture 
which the carbonic acid evolved in the course of the ex¬ 
periment might carry over. A tube containing dry chloride 
of calcium may be adapted to the neck of the flask by means 
of a perforated cork: this method will ensure greater accu¬ 
racy. The flask (whether fitted up with the tube or cotton¬ 
wool) containing the water, oxide of manganese, and 
sulphuric acid, is now to be weighed, and 100 grains of 
oxalic acid placed in it: the tube or wool must be replaced, 
and the effervescence produced be allowed to proceed as 
Ions as it will without the aid of heat: when it ceases, a 

O 7 

very gentle heat must be applied for a few minutes, and 
when cold the flask must be weighed: the loss of weight 
corresponds to the amount of peroxide present. Thus, sup¬ 
posing 


The flash, water, peroxide of manganese, sulphuric acid, 
and tube or wool, weighed ..... 
Oxalic acid added ........ 

And the weight after the operation to be . 

Loss ...... 


2000 grs. 
_100 
2100 ' 
2000 


40 


The sample under assay would contain 40 grains of peroxide 
in the 50 grains of ore employed : hence the percentage of 
pure peroxide would be 80. 



C5G 


FRESENIUS AND WILL’S METHOD. 


In case more exact results are required, the following 
plan by Fresenius and Will, may be advantageously em¬ 
ployed. The description is taken from the English edition.* 

The principle upon which this method is based has been 
applied already by Berthier and Thomson. 

The following remarks will serve to explain it. 

a. If oxalic acid (or an oxalate) is brought into contact 
with binoxide of manganese, in presence of water and excess 
of sulphuric acid, protosulphate of manganese is formed, 
and carbonic acid evolved, while the oxygen, which we 
may assume to exist in the binoxide of manganese in com¬ 
bination with the protoxide, combines with the elements of 
the oxalic acid, and thus converts the latter into carbonic 
acid. 

Mn0 2 + S0 3 + C 2 0 3 =Mn0,S0 3 4- 2CO. 

Each equivalent of available oxygen, or, what amounts to 
the same, each 1 eq. binoxide of manganese = 43’5, gives 2 
eq. carbonic acid = 44. 

b. If this process is performed in a weighed apparatus 
from which nothing except the evolved carbonic acid can 
escape, and which, at the same time, permits the complete 
expulsion of that acid, the diminution of weight will at 
once show the amount of carbonic acid which has escaped, 
and consequently, by a very simple calculation, the quantity 
of binoxide contained in the analysed manganese ore. As 
44 parts by weight of carbonic acid correspond to 43’5 of 
binoxide of manganese, the carbonic acid found need simply 
be multiplied by 43A, and the product divided by 44, or the 
carbonic acid may be multiplied by 

4fT=0'9887 

to find the corresponding amount of binoxide of manganese. 

c. But even this calculation may be avoided, by simply 
using in the operation the exact weight of ore which, if the 
latter consisted of pure binoxide, would give 100 parts of 
carbonic acid. 

The number of parts evolved of carbonic acid expresses, 

* Fresenius’s Quantitative Analysis, 4th edition, p. 615. London, Churchills. 



ANALYTICAL PROCESS. 


C57 


in that case, directly the number of parts of binoxide con¬ 
tained in 100 parts of the analysed ore. It results from b 
that 98*87 is the number required. Suppose the experiment 
is made with 0*9887 grm. of the ore, the number of centi¬ 
grammes of carbonic acid evolved in the process expresses 
directly the percentage of binoxide contained in the analysed 
manganese ore. Now, as the amount of carbonic acid 
evolved from 0*9887 grm. of manganese would be rather 
small for accurate weighing, it is advisable to take a multiple 
of this weight, and to divide afterwards the number of 
centigrammes of carbonic acid evolved from this multiple 
weight by the same number by which the unit has been 
multiplied. The multiple which answers the purpose best 
for superior ores is the triple, = 2*966 ; for inferior ores, 
I recommend the quadruple, = 3*955, or the quintuple, = 
4*9435. 

The analytical process is performed in the apparatus illus¬ 
trated in hg. 130. 

The flask A should hold, up to the neck, about 120 c. c. ; 
B about 100 c. c. The latter is half filled with sulphuric 
acid ; the tube a is closed at b with a little wax ball, or a 
very small piece of caoutchouc 
tubing, with a short piece of glass 
rod inserted in the other end. 

Place 2*966, or 3*955, or 4*9435 
grms.—according to the quality of 
the ore—in a watch-glass, and tare 
the latter most accurately on a 
delicate balance ; then remove the 
weights from the watch-glass, and 
replace them by manganese from 
the tube, very cautiously, witli the 
aid of a gentle tap with the finger, 
until the equilibrium is exactly 
restored. Transfer the weighed 
sample, with the aid of a card, to 
the flask A, add 5—6 grms. neutral oxalate of soda, or 
about 7*5 grms. neutral oxalate of potassa, in powder, and 
much water as will fill the flask to about one-third. 

u u 


Fig. 130. 



as 



























658 


TIIE ASSAY OF MANGANESE. 


Insert the cork into A, and tare the apparatus on a strong 
but delicate balance, by means of shot, and lastly tinfoil, 
not placed directly on the scale, but in an appropriate 
vessel. The tare is kept under a glass bell. Try whether 
the apparatus closes air-tight. Then make some sulphuric 
acid How from B into A , by applying suction to cl , by 
means of a caoutchouc tube. The evolution of carbonic 
acid commences immediately in a steady and uniform 
manner. When it begins to slacken, cause a fresh portion 
of sulphuric acid to pass into A, and repeat this until the 
manganese ore is completely decomposed, which, if the 
sample has been very finely pulverised, requires at the 
most about five minutes. The complete decomposition of 
the analysed ore is indicated, on the one hand, by the cessa¬ 
tion of the disengagement of carbonic acid, and its non¬ 
renewal upon the influx of a fresh portion of sulphuric acid 
into A : and, on the other hand, by the total disappearance 
of every trace of black powder from the bottom of A A 

Now cause some more sulphuric acid to pass from B 
into A , to heat the fluid in the latter, and expel the last 
traces of carbonic acid therein dissolved; remove the wax 
stopper, or India-rubber tube, from b, and apply gentle 
suction to d until the air drawn out tastes no longer of 
carbonic acid. Let the apparatus cool completely in the 
air, then place it on the balance, with the tare on the other 
scale, and restore equilibrium. The number of centi¬ 
gramme weights added, divided by 3, 4, or 5, according to 
the multiple of 0*9887 grm. used, expresses the percentage 
of binoxide contained in the analysed ore. 

In experiments made with definite quantities of the ore, 
weighing in an open watch-glass cannot well be avoided, 
and the dried manganese is thus exposed to the chance of a 
reabsorption of water from the air, which of course tends to 
interfere, to however so trifling an extent, with the accuracy 
of the results. In very precise experiments, therefore, the best 
way is to analyse an indeterminate quantity of the ore, 
and to calculate the percentage as shown above. For this 

* If the manganese ore has been pulverised in an iron mortar, a few black 
spots (particles of iron from the mortar) will often remain perceptible. 


ANALYTICAL PROCESS. 


659 


purpose, one of the little corked tubes, filled with the dry 
pulverised ore, is accurately weighed, and about 3 to 5 grins, 
(according to the quality of the ore) are transferred to the 
ilask A. By now reweighing the tube, the exact quantity 
of ore in the flask is ascertained. To facilitate this operation 
it is advisable to scratch on the tube, with a file, marks 
indicating, approximately, the various quantities which may 
be required for the analysis, according to the quality of the 
ore. 

^ ith proper skill and patience on the part of the operator, 
a good balance, and correct weights, this method gives most 
accurate and corresponding results, differing in two analyses 
of the same ore barely to the extent of 02 per cent. 

If the results of two assays differ by more than (12 per 
cent, a third experiment should be made. In laboratories, 
where analyses of manganese ores are matters of frequent 
occurrence, it will be found convenient to use an aspirator 
for sucking out the carbonic acid. In the case of very 
moist air, the error which proceeds from the fact that the 
water in the air drawn through the apparatus is retained, 
and which is usually quite inconsiderable, may now be 
increased to an important extent. Under such circumstances 
connect the end of the tube b with a chloride of calcium 
tube during the suction. 

Some ores of manganese contain carbonates of the alkaline 
earths , which of course necessitates a modification of the 
foregoing process. To ascertain whether carbonates of the 
alkaline earths are present, boil a sample of the pulverised 
ore with water, and add nitric acid. If any effervescence 
takes place, the process is modified as follows (Bohr*) :— 

After the weighed portion of ore has been introduced 
into the flask A , treat it with water, so that the flask may 
be about \ full, add a few drops of dilute sulphuric acid (1 
part, by weight, sulphuric acid, to 5 parts water) and warm 
with agitation, preferably in a water-bath. After some 
time dip a rod in and test whether the fluid possesses a 
strongly acid reaction. If it does not, add more sulphuric 
acid. As soon as the whole of the carbonates are decom- 

* Zeitschrift f. analyt . Chan. I, 48. 


u u 2 



6G0 


TIIE ASSAY OF MANGANESE. 


posed by continued heating of the acidified fluid, completely 
neutralise the excess of acid with soda solution free from 
carbonic acid, allow to cool, add the usual quantity of 
oxalate of soda, and proceed as above. 

If no soda solution free from carbonic acid is at hand, 
place the oxalate of soda or oxalic acid (about 3 grm.) 
in a small tube, and suspend this in the flask A by means of 
a thread, fastened by the cork. When the apparatus is 
tared, and it has been proved to be air-tight, release the 
thread, and proceed as above. 

In the decomposition flask place the ore and some dilute 
sulphuric acid, and add a solution of oxalic acid through 
the funnel tube ; if necessary, also dilute sulphuric acid. If 
the ore contains alkaline earthy carbonates, their carbonic 
acid may be determined in a convenient manner by this pro¬ 
cess, before the oxidation of the oxalic acid is commenced. 

BLOWPIPE REACTIONS OF MANGANESE. 

Sulphide of Manganese.— Alone , in the matrass, under¬ 
goes no change. 

In the open tube roasts slowly, but gives no sublimate. 
The roasted surface takes a bright green tinge. 

On charcoal , after complete roasting, behaves with the 
fluxes like pure oxide of manganese. 

Peroxide of Manganese. — Alone, in the matrass, when 
pure, undergoes no sensible alteration, but in general it con¬ 
tains more or less hydrate of manganese, the water of which 
may be driven off by means of heat. The more water the 
heated matter gives off, the less available oxide of manga¬ 
nese it contains. On charcoal it becomes reddish-brown in 
a good reducing flame. 

With borax and microcosmic salt it dissolves with a brisk 
effervescence, produced by disengagement of oxygen ; it then 
behaves as oxide of manganese. 

Oxide of Manganese.— Alone, the protoxide is not fusible, 
but becomes brown in a strong flame. 

With borax it forms a transparent glass, having the colour 
of amethyst, which becomes colourless in the reducing flame. 


BLOWPIPE REACTIONS OF MANGANESE. 


661 


If much oxide be present, the glass must be pressed on a cold 
body, at the instant the blast ceases. The colour returns by 
a slow cooling. 

With microcosmic salt it fuses readily, forming a trans¬ 
parent glass, which is colourless in the reducing flame, and 
amethystine in the oxidising flame. If the glass produced 
by the union of oxide of manganese with phosphoric acid 
contain so little of the former as to give no sensible reaction, 
it can be rendered evident by plunging into the bead a 
crystal of nitre. The bead swells and foams, and the froth 
becomes on cooling an amethystine or pale rose tint, accord¬ 
ing to the quantity present. 

With soda , the oxide fuses on platinum foil or wire, form¬ 
ing a transparent green glass, which becomes on cooling a 
bluish-green. This assay is best made on platinum foil. 
One-thousandth of oxide of manganese gives a very per¬ 
ceptible colour with soda. 


r 


CIIAPTEB XXIT. 


ASSAY OF COBALT AND NICKEL ORES. 

Although cobalt and nickel usually accompany each other, 
yet it will be more convenient to give the ores of both sepa¬ 
rately, commencing with those of cobalt. 

Ores of Cobalt. 

Oxide of cobalt, (CoO). 

Sulphide of cobalt, koboldine (Co 2 S 3 ). 

Sulphate of cobalt (CoO,S0 3 ). 

^ The arsenides of cobalt. 

Arsenio-sulphide, or grey cobalt (CoAs 2 + CoS 2 ). 

Arsenite of cobalt. 

Ores of Nickel. 

Oxide of nickel. 

Sulphide of nickel. 

Arsenide of nickel; kupfernickel. 

Arsenio-sulphide of nickel; grey nickel. 

Antimonio-sulphide of nickel. 

Arseniate of nickel. 

Arsenite of nickel. 

Silicate of nickel. 

Assay for Cobalt .—The analysis of cobalt ores is the most 
tedious, with the exception of those of platinum, of any that 
fall under the assayer’s notice—the greatest difficulty being 
in the separation of cobalt and nickel. The following pro¬ 
cess, however, is the most ready that has yet been devised. 
Very carefully roast, in a porcelain capsule or crucible, 100 
or more grains of the sample to be examined. (In case, 
however, any of the rich ores are under assay, 25 to 50 
grains will suffice.) When no more vapours of arsenious 
acid are evolved, add a little finely-powdered charcoal, and 
again roast, and soon until no arsenical smell is perceptible. 
Allow the roasted mass to cool, and then gently heat it in a 


ASSAY FOR COBALT. 


GG3 


flask with hydrochloric acid until all but silica is dissolved ; 
evaporate to dryness ; allow to cool; moisten with hydro¬ 
chloric acid; let stand for an hour : then add water, boil, 
and filter. To the cold filtered solution add a little hydro¬ 
chloric acid, and pass into this acidulated solution sulphu¬ 
retted hydrogen gas until in great excess ; allow the solution 
so saturated with gas to remain at rest for two or three 
hours, then filter it, add a little nitric acid to the filtered so¬ 
lution, and boil so as to peroxidise all the iron present: this 
point must be carefully attended to, and may be recognised 
by the addition of a few drops of nitric acid to the hot solu¬ 
tion giving no dark tinge. Allow the solution to cool, and 
if not quite bright, filter it. To the filtered solution add 
excess of carbonate of baryta. Iron and alumina will be 
removed after a digestion of three or four hours. Again 
filter, and to the solution add sulphide of ammonium in 
excess, gently warm and filter, wash the precipitate, dissolve 
it in hydrochloric acid ; if not bright, filter, and to the 
filtered solution add cyanide of potassium in excess, and 
boil. To the boiling solution add a little carbonate of soda 
—this will precipitate manganese if present—and filter. 
The solution now contains nothing but cobalt and nickel. 
These may be separated as follows :—Warm the solution 
and add to it excess of pulverised peroxide of mercury : this 
decomposes the potassio-cyanide of nickel, and the whole of 
the nickel precipitates, the cobalt alone remaining in solu¬ 
tion. Bemove the nickel by filtration, and neutralise as 
nearly as possible the filtered solution containing the cobalt 
by the aid of nitric acid ; then add neutral nitrate* of mer¬ 
cury solution as long as a white precipitate forms : this pre¬ 
cipitate is cyanide of mercury and cobalt. It is collected on 
a filter, well washed, dried, and then ignited, with free 
access of atmospheric air, to convert it into black per¬ 
oxide of cobalt, which is weighed. The nickel precipitate 
collected on the filter is treated in the same manner: every 
100 parts of oxide of nickel correspond to 78*7 parts 
of metallic nickel. It may be here mentioned, that cobalt 
is always estimated commercially as oxide, and nickel as 
metal. 



6)4 


THE ASSAY OF COBALT AND NICKEL. 

A method of separating these metals, given some years 
since by Liebig, consists in boiling the mixed double cya¬ 
nides of nickel and potassium and cobalt and potassium 
with oxide of mercury. Oxide of nickel is precipitated, 
while an equivalent quantity of mercury is dissolved as 
cyanide. The method certainly gives good results, but is 
not free from objection. Long boiling is necessary before 
the precipitation is complete, and it is difficult to prevent 
bumping during ebullition. The excess of oxide of mercury 
must be separated from the oxide of nickel by a special 
operation, and the nickel afterwards again precipitated by 
caustic alkali. 

According to Wolcott Gibbs,* these inconveniences may 
be completely avoided by employing, instead of the oxide 
alone, a solution of the oxide in the cyanide of mercury. 
When this solution is added to a hot solution of the double 
cyanide of nickel and potassium, the whole of the nickel is 
immediately thrown down as a pale green hydrate of the 
protoxide. Under the same circumstances cobalt is not 
precipitated from the double cyanide of cobalt and potas¬ 
sium. Mr. W. N. Hill, who has repeatedly employed this 
method and carefully tested it, has found that the separation 
effected is complete. No cobalt can be detected in the pre¬ 
cipitated oxide of nickel by the blowpipe, nor can the nickel 
be detected in the cobalt (finally separated as oxide) by 
Plattner’s process with the gold bead. The solution of 
oxide of mercury is easily obtained by boiling the oxide 
with a strong solution of the cyanide, and filtering. Accord¬ 
ing to Kuhn, the cyanide formed in this manner has the 
formula HgCy +*3HgO. The hydrated oxide of nickel 
precipitated may be filtered off, washed, dried, ignited, 
and weighed. The cobalt is more readily and conveniently 
determined bv difference, when, as it is always possible, the 
two metals have been weighed together as sulphates. I am 
not prepared to say that this modification of Liebig’s method 
of separating nickel and cobalt gives better results than Stro- 
meyer’s process by means of nitrite of potassium, but it is at 
least very much more convenient, and requires much less 

* Chemical Ncivs, March 17, 1865. 


SEPARATION OF COBALT FROM NICKEL. 


665 


time. The complete precipitation of cobalt in the form of 
Co 2 0 3 ,2N0 3 + 3K0,N0 3 usually requires at least forty-eight 
hours, and rarely succeeds perfectly except in experienced 
hands. 

M. Terreil has proposed a very excellent method for sepa¬ 
rating these two metals. The author’s method is founded— 

1, on the insolubility of roseocobaltic hydrochlorate in acid 
liquids and ammoniacal salts, discovered by M. Fremy; 

2, on the rapid transformation of ordinary salts of cobalt 
into roseocobaltic salts, under the double influence of am¬ 
monia and oxidising bodies—such as permanganate of 
potash and alkaline hypochlorites; 3, on the complete pre¬ 
cipitation of manganese in ammoniacal liquids by alkaline 
hypochlorites, and permanganate of potash. 

To separate cobalt from nickel, operate in the following 
manner :— 

To the solution of the two metals add an excess of 
ammonia, which re-dissolves the two oxides; add to the 
hot ammoniacal liquid a solution of permanganate of potash, 
sufficient to cause the liquid to remain coloured violet for a 
few instants by the excess of permanganate. Boil the liquid 
for a few minutes, then add a slight excess of hydrochloric 
acid, to re-dissolve the oxide of manganese which will have 
formed. Heat the liquid gently for twenty or twenty-five 
minutes, then let it stand for about twenty-four hours. All 
the cobalt will then be deposited in the form of a beautiful 
red-violet crystalline powder ; the precipitate is roseocobaltic 
hydrochlorate, which collect on a weighed fdter, wash it on 
the fdter with cold water, then with diluted hydrochloric 
acid, or with a solution of ammoniacal salt, and then with 
ordinary alcohol, which frees it from ammoniacal salt. Dry 
it at 110°, and weigh. 100 parts of roseocobaltic hydro¬ 
chlorate correspond to 22*761 of metallic cobalt, or to 
28*959 of protoxide of cobalt. 

It is, however, better to take a given quantity of the 
roseocobaltic salt, and reduce it by dry hydrogen; this 
leaves perfectly pure cobalt to be weighed. 

Next boil the solution containing nickel to expel the 
alcohol which has been introduced in washing the cobaltic 




(>66 THE ASSAY OF COBALT AND NICKEL. 

salt; saturate it with ammonia, add another small excess 
of permanganate of potash, and boil. All the manganese 
will be precipitated ; filter the liquid, and all the nickel 
will be found in the filtrate, from which it may easily be 
separated in the state of sulphide, and then transformed into 
oxide. 

By this process the presence of a ten-thousandth part of 
cobalt in a salt of nickel may be ascertained. 

In this operation an alkaline hypochlorite may take the 
place of the permanganate of potash, but then the deposit of 
roseocobaltic salt takes place with extreme slowness, and 
several days are required to complete it. This reagent is 
preferable to permanganate when manganese is to be sepa¬ 
rated from nickel and cobalt. 

Should the substance to be analysed contain at the same 
time cobalt, nickel, and manganese, the latter may be esti¬ 
mated by operating as above, but using given quantities of 
permanganate and potash estimated beforehand. Lastly, 
the precipitate of oxide of manganese should be collected, 
washed, dried, and calcined ; from the weight of red oxide 
obtained, subtract the amount of manganese added in the 
state of permanganate. 

The separation of manganese from cobalt or nickel is 
extremely easy ; it may be effected equally well by means 
of alkaline hypochlorites or permanganate of potash, which 
completely precipitate manganese from ammoniacal solutions, 
and which, under the same conditions, precipitate neither 
cobalt nor nickel, which remain in the filtered liquids. The 
method of operating is exactly the same as that above 
described. 


BLOWPIPE KEACTIONS OF COBALT. 

Sulphide of Cobalt. —In the matrass, gives no volatile 
substance, and does not decrepitate. In the open tube 
gives sulphurous acid, and a white sublimate, which consists 
of drops perceptible by the microscope ; they are concen¬ 
trated sulphuric acid. There are no traces of arsenic. 

With the fluxes, the reactions of cobalt so predominate 
that it is impossible to discover those of iron and copper ; 


BLOWPIPE REACTIONS OF COBALT. 


G67 


but if it be fused many times with borax, in the exterior 
flame (that is, the grey bead produced by fusion on char¬ 
coal of the mineral itself), the borax removes the cobalt, and 
the copper concentrates ; so that when the mass is fused 
with microcosmic salt, and exposed to the reducing flame, 
the red colour of the oxide of copper is produced, tinged, 
however, by the cobalt blue. 

Arsenical Cobalt. — Alone, in the open tube, gives an 
abundance of arsenious acid with great facility. In the 
matrass , some species give a little metallic arsenic; others 
give none. 

On charcoal all disengage an arsenical smoke and odour, 
and give by fusion a white metallic bead. 

Cobalt Glance (Tunaberg). — Alone , in the matrass suffers 
no change. 

In the open tube , roasts with difficulty, giving no arsenious 
acid but by a very strong fire, but disengaging sulphurous 
acid. 

On charcoal , gives an abundance of fumes, and enters into 
fusion after some considerable roasting ; it then behaves as 
arsenical cobalt. 

Black Oxide oe Cobalt. — Alone , gives a little empyreu- 
matic water. 

On charcoal , gives traces of arsenic but does not fuse. 

Dissolves in borax and microcosmic salt, giving so deep a 
blue as to disguise all other action. 

It is infusible with soda, and generally gives on the pla¬ 
tinum wire a mass strongly tinted green by manganese. 

Arseniate of Cobalt. — Alone , in the matrass, gives off 
water and becomes brown, but furnishes no sublimate. 

On charcoal , gives off much vapour, and a smell of arsenic. 
Fuses in a good reducing flame, and is converted into 
arsenical cobalt. 

Oxide of Cobalt. — Alone , suffers no change. 

With borax it readily fuses, forming a fine transparent 
blue glass, which does not become opaque by flaming. A 
very small quantity colours the glass completely blue, and a 
large quantity imparts so deep a colour as to make it appear 
black. 



668 


THE ASSAY OF COBALT AND NICKEL. 


With microcosmic salt the appearances are the same as 
with borax. 

Soda dissolves but a very small quantity on the platinum 
wire: the fused mass is pale red by transmitted light, and 
becomes grey on cooling. 

Carbonate of potash dissolves a larger quantity of this 
oxide, forming a black mass, without the slightest mixture 
of red. This reaction presents a method of distinguishing 
potash from soda. 

The oxide of cobalt is very readily reduced on charcoal 
in the interior flame, either by an alkali or an alkaline salt. 
After the soda and charcoal are washed away, a grey metallic 
powder is obtained, which takes the metallic lustre under 
the burnisher. 


BLOWPIFE REACTIONS OF NICKEL. 

Sulphide of Nickel.— In the open tube gives sulphurous 
acid, becomes black, but does not change form. On char¬ 
coal, gives, by aid of a good flame, a mass conglomerated by 
semi-fusion. It is metallic, malleable, and is pure nickel. 

After roasting in the open air, it behaves with fluxes like 
oxide of nickel. 

Arsenical Nickel, in the matrass, gives nothing volatile; 
semifuses at the temperature which softens glass, and a 
deposit of arsenious acid is formed on the sides of the 
matrass: this is owing to the included air. 

It fuses on charcoal , with a vapour and arsenical odour, 
and a white metallic globule. 

In the open tube it roasts easily, with the formation of a 
large quantity of arsenious acid; the residue is a yellowish- 
green substance, which, on roasting afresh on charcoal, and 
fusion with soda and borax, gives a tolerably malleable 
metallic grain, and is very magnetic. 

After roasting, it behaves with the fluxes like oxide of 
nickel, and generally gives a glass, which is slightly blue, 
owing to the presence of a small quantity of cobalt. 

Oxide of Nickel. — Alone , is not acted upon. 

With borax it fuses very readily, producing an orange- 


BLOWPIPE REACTIONS OF NICKEL. 


669 


yellow or red glass, which, by cooling, becomes yellowish 
or nearly colourless. A larger quantity of the oxide gives 
a glass which, when liquid, is deep brown, but which, on 
cooling, becomes dull red and transparent. This colour is 
destroyed in the reducing flame, and the glass becomes grey, 
on account of particles of metallic nickel being disseminated 
through it. 

With microcosmic salt it fuses, giving rise to the same 
phenomena as with borax; but the colour nearly, if not 
quite, disappears on cooling. It behaves alike in the oxi¬ 
dising and reducing flames, by which reaction it is distin¬ 
guished from iron. Tin produces, at first, no change; but 
after a short time the nickel precipitates, and the colour dis¬ 
appears. If cobalt be present, it can then be perceived; 
but the blue glass is opaque, and cannot be so well distin¬ 
guished with this flux as when treated in the same manner 
with borax. 

Soda does not dissolve oxide of nickel. A large quantity 
of this flux, however, causes the charcoal to absorb it; it 
is then reduced, and furnishes, by washing, small, white, 
brilliant, metallic particles, which are as strongly attracted 
by the magnet as wrought iron. 

The following is Plattner’s method for detecting nickel, 
when contained in large quantities of cobalt:— 

Fuse in the oxidising flame a moderate quantity of borax 
to a bead in the loop of platinum wire, with sufficient oxide 
of cobalt to give an opaque glass ; remove the assay, and 
prepare one or two similar beads, and place the whole in a 
charcoal cavity, with a button of pure gold weighing from 
fifty to eighty milligrammes. The operator must now heat 
in the reducing flame, until he is satisfied that the whole of 
the nickel is in a metallic state ; the charcoal during the 
action must be inclined alternately backwards and forwards, 
so that the gold button may flow through the matter glass, 
and form an alloy with the reduced particles of nickel. 
When the golden globule solidifies, it must be extracted 
with a forceps, placed between paper, and struck with a 
hammer, so as to detach all the adhering vitreous parts. 
The auriferous button, which has become more or less grey, 



670 


T1IE ASSAY OF COBALT AND NICKEL. 


from the presence of nickel, and also more brittle than pure 
gold, is now to be mixed with microcosmic salt, and heated 
for some time in the oxidating flame. If the borax-glass 
has not been in the first instance oversaturated with oxide 
of cobalt, a bead will be now obtained which is coloured 
only by oxide of nickel, and will therefore appear brownish- 
red while hot, and when cold reddish-yellow. Should por¬ 
tions of oxide of cobalt be also reduced, as the cobalt is 
oxidised before the nickel, either a blue glass, coloured by 
oxide of cobalt, or a green one—if some nickel was also 
oxidised—will be obtained. In either case the glass must 
be separated from the button, mixed with more microcosmic 
salt, and heated in the oxidising flame until it acquires a 
tinge. If the borax glass had not been oversaturated at the 
commencement, the colour now obtained will proceed from 
nickel, although the oxide of cobalt contains a trace only; 
but if oxide of nickel be not present, the microcosmic bead 
remains perfectly colourless. 




671 


CHAPTER XXIII. 

THE ASSAY OP SULPHUR. 

The only commercially valuable Sulphur-minerals are :—■ 

I. Sulphurous Earth (native sulphur). 

In Sicily these minerals are divided into live classes :— 

1. Very rich ores, containing 32—34 p.c. sulphur 

2. Rich „ „ 24—26 „ 

3. Good „ ,, 16—18 ,, 

4. Middling „ ,, 8— 9 ,, 

5. Poor „ „ 3— 5 „ 

II. Iron and Copper Pyrites (FeS 2 ), (Cu 2 S, Fe 2 S 3 ). 

These ores are used to a great extent for the manufacture 

of sulphuric acid. 

In order to approximatively estimate the value of these 
ores for such manufacture, the following 

DISTILLING ASSAY 

may be used. 

A certain quantity of the pulverised ore is heated in a 
retort, which is furnished with a receiver. The retort may 
be of glass if the ore is sulphurous earth, but earthen re¬ 
torts must be employed if pyrites are to be assayed, as 
the temperature required is much higher (full red heat) 
than is used for distilling sulphurous earth. If assaying rich 
pyrites, they must be mixed with quartz sand, as without 
such mixture a cementation of the ore will take place, which 
would hinder the sublimation of the sulphur. 

The retort is then heated, gradually raising the tempera¬ 
ture, till no more sulphur is evolved. The latter will 
collect in the receiver, which may be, in all cases, of glass, 
and must be kept cool. 


672 


TIIE ASSAY OF SULPHUR. 


The sulphur derived from sulphurous earth is generally 
pure, but that from pyrites frequently contains arsenic and 
selenium, and sometimes traces of thallium. 

The manufacture of sulphuric acid is effected by roasting 
the sulphur-minerals in the presence of air, in some sort of 
muffle, or in other furnaces. The resulting sulphurous acid 
is conducted into closed chambers, where it is converted into 
sulphuric acid. 

The yield of sulphur by this process is always larger than 
that obtained by the above distilling process, and it would 
be possible to extract by it the whole of the sulphur, or 
nearly so, if economical considerations did not prevent this, 
as the separation of the last remaining sulphur requires a 
disproportionate amount of fuel. 

In order to fully ascertain the value of a sulphur ore for 
the manufacture of sulphuric acid, four assays are required. 

1. A determination of the whole amount of sulphur con¬ 
tained in the ore. This must be done by an analysis. 

2. A determination of that amount of sulphur which may 
be obtained by roasting the ore. For this purpose the ore 
is to be roasted on a small scale, but as nearly as possible as 
it is done by the manufacturer. 

3. A determination of that portion of sulphur which 
remains in the roasted ore. This must be also done by an 
analysis. 

4. An analysis of the sulphur obtained, as foreign sub¬ 
stances contained in it, for instance arsenic, modify its value. 

THE ASSAY OF SULFIIUR IX THE WET WAY. 

Act upon 50 grains by repeated doses of aqua regia , or, 
better still, strong nitric acid and chlorate of potash, until 
the ore is entirely decomposed, and if any sulphur remains 
unacted on, it is quite bright and of a fine amber colour, as 
described in the Humid Assay of Copper Ores of the Second 
and Third Classes. When all action has ceased, carefully 
filter, wash, dry, and weigh the residue; ignite it in a small 
porcelain dish, weigh again, and the loss of weight will be 
sulphur. Add to the filtered solution chloride of barium, 


TIIE ASSAY OF SULPHUR IN THE WET WAY. 


673 


until no further precipitation takes place; let the whole stand 
in a warm situation for an hour or so ; collect the precipitate 
on a filter, wash, dry, and ignite it Every 116 parts of this 
precipitate of sulphate of baryta correspond to 16 parts of 
sulphur. The quantity obtained in this manner, added to 
that obtained in the first part of the operation by the 
ignition of the insoluble residue, will give the amount of 
sulphur in the portion of ore operated on. 


x x 


674 


CHAPTER XXIV. 

DISCRIMINATION OF GEMS AND FRECIOUS STONES. 

In order to explain the introduction of the present chap¬ 
ter into this work, it may be stated, that as many of the 
precious stones are found in connection with gold, and as 
the alluvial and other sources of that metal have of late 
been so wonderfully multiplied, and as diamonds, rubies, 
emeralds, &c., have by careful examination and research 
been discovered in Australia and elsewhere, it has been 
thought advisable to devote a chapter to the elucidation of 
this important subject; in the hope that, with the instruc¬ 
tion here given, those who may cast their lots, either tem¬ 
porarily or permanently, in positions geologically likely to 
furnish the subjects treated under the present heading, may 
find themselves materially assisted in the discovery of 
minerals, on the discrimination of which but little has been 
popularly written. 

The principal sources of recognition are colour, crystalline 
form, specific gravity, and hardness. In the present chapter 
will be introduced all the most constantly occurring natural 
forms of the gems and precious stones mentioned. 

The specific gravity or density of a substance is the pro¬ 
portion of its weight to its volume, and it forms a charac¬ 
teristic property of substances. To express the specific 
gravity in figures it is requisite to compare the density of 
one substance with that of another, and water at 4° C. is 
generally adopted as a standard. The specific gravity or 
density of a substance, therefore, indicates how much a sub¬ 
stance is heavier than an equal volume of water. 

One cubic centimetre of iron weighs 7*8 grammes, and 


GEMS AND PRECIOUS STONES. 


G75 


an equal volume of water = 1 gr.; the specific gravity of 
iron is, therefore, said to be 7*8. 

The specific gravity of a substance may be calculated by 
dividing its absolute weight by the weight of a corresponding 
volume of water. 

It may be determined at follows, if the sample be of suffi¬ 
cient size to suspend from the pan of a balance by means of 
a fibre of silk ; if not, another mode must be adopted, which 
will be pointed out as we proceed. 

If the mineral can be suspended, attach it by a short 
fibre of silk to one of the pans of a delicate balance, and 
ascertain its weight; then immerse it (still suspended to the 
pan) in distilled water of the temperature 60° Fahr., and 
then note its weight; it will be found to have lost a certain 
amount, which will correspond to the weight of the bulk of 
water it has displaced. Divide its weight in air by the loss 
of weight in water, and the quotient will be the required 
specific gravity. This will be more readily understood by 
an example. Suppose we find the mineral to weigh 80 grs. 
in the air, and only 60 in water ; the loss = 80 — 66 = 14. 
We must now divide 80 by 14, thus = 5 7, which is 
about the specific gravity of a sample of bournonite. 

We have now the second case to consider; the mineral 
may be in very small fragments, or it may even be in 
powder, in which case its specific gravity must be determined 
thus:— 

A small bottle (the ordinary specific gravity bottle is well 
suited for the purpose), filled with water, is placed on one of 
the pans of a delicate balance, and its weight ascertained. 
The mineral in fragments, or even in powder, whose specific 
gravity is to be determined,. is put on the same pan, and 
the weight of both the filled bottle and the mineral is 
ascertained. 

The mineral is then introduced into the bottle, when 
part of the water will flow out corresponding to the volume 
of the mineral, the weight of which may be ascertained by 
again weighing the bottle, filled partly with water, and 
partly with mineral. 


G7C> 


GEMS AND PRECIOUS STONES. 


The following example will suffice to render this clearer:— 

Suppose the bottle filled with water to weigh . . . GOO grs. 

And the mineral weighing.. .100 

Weight of both ..... 000 

W eight of the bottle when containing the mineral and part 
of the original water ....... GOO 

Leaves the absolute weight of the water expelled from the 
bottle by the mineral ....... 40 

Therefore the specific gravity of the mineral equals -A°o°- = 2*5 

COLOURLESS STONES. 

The Diamond. —Specific gravity, 3*48 to 3*52 ; hardness, 
10. The diamond is the hardest of all known substances. 
The diamond is the only substance which is capable of cutting 
glass, although most gems will scratch glass; lienee it is the 
utmost term of hardness. When cut and polished, it is the 
most brilliant gem. It frequently becomes phosphorescent 
on exposure to light. The greater part of diamonds are 
limpid and colourless, but many coloured specimens are 
found ; as rose, yellow, orange, blue, green, brown, or even 
black. It sometimes occurs in regular crystals, octoliedrons, 
dodecahedrons, and more complex forms : see figs. 131,132, 
133, 134. 



The crystalline faces are often curved. The cleavage is 
octohedral and highly perfect: hence, although diamonds 






COLOURLESS STONES. 


677 


are so exceedingly hard, they are very brittle, owing to their 
tendency to facile cleavage. Like most gems, they become 
electrical by friction ; but it has been remarked that other 
gems do not, unless they have been previously polished. 

Composition (C):—Pure carbon. 

Quartz .—Specific gravity, 2-55 to 2*7 ; hardness, 7. 
Quartz occurs in many forms, and has often by inex¬ 
perienced persons been mistaken for the diamond, owing to 
the lustre of its crystals and its considerable hardness. It 
however, can always be distinguished from the diamond by 
its crystalline faces, hardness, and specific gravity (see ex¬ 
ample in Table I.) 

It usually occurs in six-sided prisms, more or less modified, 
terminated with six-sided pyramids. Traces of cleavage are 


seldom or ever apparent. The following are some of its 
salient forms (figs. 135, lo6, 137, lob, 131), 140, 141): 


Fig. 137 








(578 


GEMS AND PKECJOUS STONES. 


Fig. 140. 



Some crystals are as pellucid as glass ; others, however, 
assume all the shades of colour mentioned in the case of the 
diamond. 

Composition (Si0 3 ):—Pure silica or silicic acid. 

White Zircon .—Specific gravity, 4 44 to 4 -8 ; hardness, 
7’5. This stone is often found crystallised in nature in 
four-sided prisms, terminated by four-sided or rhomboidal 
or triangular pyramids, and other forms : see figs. 142, 143, 
144, 145, 146, 147. 


Fig. 143. 


Fig. 144. 



These stones are often employed in jewellery under the 
name of 4 rough diamonds.’ They often occur brownish-red 
and brown, red, yellow, and grey: these varieties will be 
treated under their appropriate heads. It can be readily 
distinguished from the diamond and quartz by hardness and 
specific gravity ; also by the action of strong hydrochloric 







COLOURLESS STONES. 


67!) 


acid, which, if dropped on the diamond or quartz, and 
allowed to remain for a little time, produces no change, but 
if a zircon be so treated, the spot on which the acid was 
placed remains dull. 


Composition (Zr 2 0 3; Si0 3 ):— 

Zirconia.07-2 

Silicic acid .335 

100 7 

White Sapphire. —Specific gravity, 3’97 to 4’27 ; hard¬ 
ness, 9. This stone, in hardness, is next to the diamond. 
It occurs variously coloured; other colours will be discussed 
under their appropriate heads. It crystallises in the rhom- 
bohedric system, usually in six-sided prisms, but often so 
very rough as not to be readily distinguishable. May be 
distinguished by gravity and hardness from all the preceding. 

Composition (A1 2 0 3 ) :—Pure alumina. 

White Topaz. —Specific gravity, 3-54 ; hardness, 9. This 
variety of topaz, known for its limpidity by the term ‘ gouttes 
d’eau,’ when polished, has nearly the same lustre as the 
diamond: the topaz, however, occurs of many colours—see 
hereafter. It crystallises in the right rectangular prismatic 
system. The following are some of its natural forms :—figs. 
148, 149, 150, 151, 152, 153. 

It is readily rendered electric, and retains its electricity 
for a very considerable time: it is also pyro-electric, or 
becomes electric when heated,— a property by which it is 
distinguished from the diamond, its specific gravity being 



Fig. 145. 













G80 


GEMS AND l’RECIOUS STONES. 


so similar that it cannot be made available as a means of 
discriminating between the two stones. From the other 
stones in this group, with the exception of the sapphire, it 


Fig. 148 



Fig. 151. 



Fig. 149. 



Fig. 152. 



Fig. 150. 



Fig. 153. 



is readily distinguished by its hardness and gravity, and from 
the latter by its gravity and pyro-electricity. 

Composition :— 


Silica . 

Alumina 

Fluorine 


.34-2 

57*5 

7*8 

99-5 


Example of the use of Table I *—A colourless stone, 
weighing 40 grains in air, is reduced to 24’43 in water. 
Look in the first column to 40, and then trace along its 
horizontal line until a number very nearly approaching 
24-43 is found ; refer then to the heading of the table, above 
the number found, and the name there expressed will be 
that of the stone examined. Supposing, however, the 
* The Tables of Comparative Weights were calculated by Braid. 
























COLOURLESS STONES. 


681 


weight of the stone be 41 grains, still the number 24‘43 will 
be the nearest in the table, and *611 must be added to it, as 
that sum woidd be the weight of 41 grains of quartz or 
water. From the numbers obtained by calculation, also can 
the specific gravity be determined. If this course be pur¬ 
sued, refer to the bottom line of the table for corresponding 
number, and to the heading of the table for name of stone. 
When the weight is any even number of grains (that is, 
without fractions), the readiest way is to refer to the table 
(first column), for the number of grains, and then to the hori¬ 
zontal line to corresponding number obtained, which is the 
weight in water. 


Table I. 

Comparative Table of the Weights of colourless Stones 
weighed in Air and Water. 


Weight 
in Air 

Grains 



Weight in Water 


White 

White 

White 

White 

White 

Zircon 

Sapphire 

Topaz 

Diamond 

Quartz 

1 

0*775 

0*766 

0*716 

0*715 

0611 

4 

3*10 

3*06 

286 

2*86 

2*42 

8 

6*20 

6*12 

5*72 

5*72 

4 86 

12 

9*30 

9*18 

8*58 

8*58 

7*31 

16 

12*40 

12*25 

11*55 

11*45 

9*75 

20 

15*50 

15*31 

14*42 

14*31 

12*19 

24 

18*60 

18*37 

17*28 

17*17 

14*64 

28 

21*70 

21*44 

20*15 

20*13 

17*08 

32 

24*80 

24*51 

23 01 

22*90 

19*53 

36 

27*90 

27*57 

25*88 

25 76 

U 98 

40 

31*00 

30*64 

28*75 

28*63 

24*43 

44 

34*10 

33*71 

31*61 

31*49 

26 88 

48 

37*20 

36*76 

34*47 

34*35 

29*32 

52 

40*30 

39*82 

37*34 

37*21 

31*77 

56 

43 40 

42*89 

40*20 

40*17 

34*21 

60 

46*50 

45*95 

43 06 

42 94 

36 66 

64 

49 60 

49 01 

45*93 

45*80 

39*11 

68 

52*70 

52*07 

484 0 

48*66 

41*56 

72 

55*80 

55*14 

51*77 

51 *52 

44*00 

76 

58*90 

58*21 

54 63 

54*38 

46*44 

80 

62*00 

61*28 

57*49 

57*24 

48*88 

84 

65*10 

64*34 

60*35 

6>12 

51*32 

88 

68*20 

67*41 

63*22 

62*97 

53*76 

92 

71*30 

70*47 

66*08 

65 33 

56*21 

96 

74*40 

73 54 

68*94 

68*69 

58*65 

100 

77*50 

76*60 

71*80 

71*55 

61*09 

Specific 

Gravity 

J 444 

4*27 

3*54 

3*52 

2*55 










































682 


GEMS AND PRECIOUS STONES. 


Diamond and topaz, however, have very nearly equal 
density, and a second characteristic must be had recourse to, 
in order to determine the nature of two stones which have 
an equal weight in water. This auxiliary character is the 
development of electricity by heat, a phenomenon exhibited 
by the topaz but not by the diamond. The test of hardness 
may be also resorted to. 


YELLOW STONES. 


Yellow Zircon {Jargon ).—The crystalline form, charac¬ 
teristics, and composition of this stone have been described 
under the head 4 White Zircon.’ 

Yellow Sapphire. —Characteristics, &c. described under 
4 White Sapphire.’ 

Cymophane (Chrysoberyl ).—Specific gravity, 3‘65 to 3-89 ; 
hardness, 8*5. The cymophane is nearly as hard as the 
sapphire, harder than the topaz and the emerald : it readily 
scratches quartz. Its colour is greenish-yellow, and has 


Eig. 155. 



been placed in the list of yellow stones rather than green, 
because usually the yellowish tint is most decided. This 









YELLOW STONES. 


08 3 


tint, which is very agreeable in itself, is often relieved by a 
small spot of light ol a bluish-white tinge, which moves 
from point to point of the stone as the position of the latter 
is varied. It is rarely found in regular crystals, but more 
generally occurs in rolled and rounded masses. For some 
of its forms, however, see figs. 154, 155, 156, and 157. 

Composition :—No. 1 is a sample from the Brazils ; No. 
2, from Siberia. 


l 2 


Alumina . 

• 

. 78-10 

78-92 

Glucina . 

# 

. 17-94 

18-02 

Oxide of iron . 

• 

. 4-40 

312 

Oxide of chromium . 


# - 

0-36 

Oxides of copper and lead 

100-50 

0-29 

100-71 


Yellow Topaz .—The general characteristics of this stone 
are described under 4 White Topaz.’ 

Yellow Tourmaline .—Specific gravity, 3-00—3*22; hard¬ 
ness, 7—7'5. The tourmaline becomes electrical by heat; 
one portion of a crystal attracts light bodies, the other 
repels them. Its colour is very varied. The tourmaline 
lias a vitreous fracture. It occurs in semicrystalline prisms 
of irregular form, generally deeply striated, and in prisms 
of six or more sides, variously terminated, one end usually 
differing from the other. 

Figs. 158, 159, 160, 161, 162, and 163, represent some 
of the forms of this mineral. 


Fig. 158. Fig. 159. 












G84 


GEMS AND PRECIOUS STONES. 


Fig. 160 . Fig. 161 . 



Yellow Emerald .—Specific gravity, 2-73—2*76 ; hard¬ 
ness, 7*5—8. The emerald occurs of many colours: its 



tint par excellence is green; but there are many varieties 
tinged more or less yellow or blue, and they even occur 

























YELLOW STONES. 


G85 


white. Its fracture is vitreous, brilliant, and undulating. 
Its common form is the hexahedral prism, sometimes deeply 
striated longitudinally. It readily cleaves parallel to all 
the planes of its primary form—the hexahedral prism. 




Fig. 170. 


Fig. 1G9. 




The above are some of the forms it assumes: figs. 164, 
165, 166, 167, 168, 169, and 170. 

Composition :— 


Glucina 

Silica 

Alumina . 
Oxide of iron 


15- 50 
66-45 

16- 75 
•60 

99-30 


The green varieties contain a small quantity of oxide of 
chromium. 

Yellow Quartz .—For the characteristics, hardness, &c. of 
this mineral, see ‘White Quartz.’ 

















GSG 


GEMS AND PRECIOUS STONES. 


Comparative Table of the Weights of yellow Stones 
weighed in Air and Water. 


Weight 
in air 

Grains. 

Weights in Water 

Yellow 

Zircon 

Yellow 

Sapphire 

Yellow 

Cymophane 

Yellow 

Topaz 

Yellow 

Tourmaline 

Yellow 

Emerald 

Yellow 

Quartz 

1 

0-775 

0-766 

9-738 

0-716 

0-690 

0-633 

0-611 

4 

310 

3-06 

2-95 

2-86 

276 

2-53 

2-42 

8 

6-20 

6-12 

5-90 

5-72 

552 

5-06 

4-86 

12 

9-30 

9-18 

8-85 

8-58 

8-28 

7-59 

7-31 

16 

12-40 

12-25 

11-80 

11-55 

11-04 

10-12 

9-75 

20 

15 50 

15-31 

14-75 

14-42 

13-80 

12-65 

1219 

24 

18-60 

18-07 

17-70 

17-28 

16-56 

15-19 

1404 

28 

21-70 

21-44 

20-65 

20-15 

19-32 

17-72 

1708 

32 

24-80 

24-51 

23-60 

23-01 

20-08 

20-25 

19-53 

36 

27-90 

27*57 

26-55 

25-88 

24-84 

22-77 

21-98 

40 

31-00 

30-64 

29-50 

29-75 

27-60 

25-30 

24-43 

44 

3410 

33-71 

32-45 

31-61 

30-36 

27-83 

26-88 

48 

37-20 

36-76 

35-40 

34-47 

33-12 

30-36 

29-32 

52 

40-30 

39-82 

38-35 

37-34 

35-88 

32-89 

31-77 

56 

43-40 

42-89 

41-30 

40-20 

38-64 

35-43 

34-21 

60 

46-50 

45-95 

44 25 

43-06 

41-40 

37-94 

36 66 

64 

49-60 

49-01 

47-20 

45-93 

44-16 

40-47 

39-11 

68 

52-70 

52-08 

50-15 

48-90 

46-92 

4300 

41-56 

72 

55-80 

55-14 

53-10 

51-77 

49-68 

45-53 

4400 

76 

58-90 

58-21 

56-05 

54-63 

52-44 

48-07 

46-44 

80 

62-00 

61-28 

59-00 

57-49 

55-20 

50-60 

48-88 

84 

65-10 

64-34 

61-95 

60-35 

57-96 

5313 

51-32 

88 

68-20 

67-41 

64-90 

63-22 

60-72 

55-66 

53-76 

92 

71-30 

70-47 

67-85 

66-08 

63-48 

58-19 

56-21 

96 

74-40 

73-54 

70-80 

68-94 

66-24 

60-72 

58-65 

100 

77-50 

76-60 

73-75 

71-80 

69-00 

63-25 

61-09 

Specific 

Gravity 

14-44 

4-27 

3-89 

3-53 

3-22 

2-72 

2-55 


BROWN AND FLAME-COLOURED STONES. 

Zircon [Hyacinth ).—For characteristics, &c. see 4 White 
Zircon.’ 

Vermeil Garnet , Noble Garnet, Almandine .—Specific 
gravity, 4—4*2 ; hardness, 6’5—75. There are very many 
varieties of garnet, variously coloured ; but their crystalline 

form—a rhombic dodecahedron, more or less modified_is 

a distinguishing characteristic. The colouring matter of 
the garnet is iron. The following are some of its crystal¬ 
line forms : figs. 171, 172, 173, i74, and 175 :— 















































BROWN AND FLAME-COLOURED STONES. 


G87 




Fig. 174. 



Composition :— 

Silica 

Alumina . 

Oxide of iron 
Oxide of manganese . 


Fig. 17o. 



. 33-75 
. 27*25 
. 3600 

* 25 

07*25 








G88 


GEMS AND PRECIOUS STONES. 


Comparative Table of the Weights of brownish and flame- 
coloured Stones weighed in Air and Water. 


Weight in Air 

Grains 

Weight in Water. 

. 9 

Hyacinthine 

Zircon 

Vermeil 

Garnet 

Essonite 

Tourmaline 

1 

0-775 

0-750 

0-710 

0-690 

4 

3-10 

300 

2-87 

2-76 

8 

6-20 

600 

5-74 

5-52 

12 

9-30 

9-00 

8-61 

8-28 

16 

12-40 

12-00 

11-48 

11-04 

20 

15-50 

15 00 

14-35 

13-80 

24 

18-60 

18-00 

17-22 

16-56 

28 

21-70 

21-00 

20-09 

19-32 

32 

24-80 

24-00 

22-96 

22-08 

30 

27-90 

27-00 

25-83 

24-84 

40 

31-30 

30 00 

28-70 

27-60 

44 

34-10 

3300 

31-57 

30-36 

48 

37-20 

36 00 

34 44 

3312 

52 

40-30 

39 00 

37-31 

35-88 

56 

43-40 

42-00 

40-18 

38-64 

60 

46-50 

4500 

43-05 

41-40 

64 

49-60 

48-00 

45-92 

. 4416 

68 

52-70 

5100 

48-79 

46-92 

72 

55-80 

54-00 

51-66 

49-68 

76 

58 90 

57-00 

54-53 

52-44 

80 

61-00 

6000 

57-40 

55-20 

84 

65-10 

63 00 

60-27 

57-96 

88 

68-20 

66-00 

6314 

60-72 

92 

71-30 

G9-00 

6601 

63-48 

96 

74-40 

72-00 

68-88 

66-24 

100 

77-50 

7500 

71-75 

6900 

Specific 

1 4-44 

4-00 

3-54 

3-22 

Gravity 

J 





Essonite , Cinnamon Stone .—Specific gravity, 3’5 to 3'6. 
This stone has an agreeable orange-yellow tinge, which 
becomes a warm and brilliant tint when the mass is large. 
This stone is not usually found crystalline, but in irregular 
forms and masses, which are characterised by fissures in all 
directions. 

Composition :— 

Silica .... 

Alumina .... 

Lime. 

Oxide of iron with small 
Potash and Magnesia 


Tourmaline .—For the characteristics of this mineral see 
4 Yellow Tourmaline.’ 


. 38-80 
. 21-20 
. 31-25 
quantities ofj^ 

07-75 
































RED AND ROSE-COLOURED STONES. 


680 


RED AND ROSE-COLOURED STONES. 

Reel Sapphire. —For characteristics, crystalline form, &c., 
see 4 White Sapphire.’ 

Deep Red Garnet , Noble Garnet. —For characteristics, 
&c., see 4 Vermeil Garnet.’ 

Ruby [Spinel). —Specific gravity, 35—3’6 ; hardness, 8. 
The ruby readily scratches quartz, but is scratched by the 
sapphire. Its special colour is red, approaching a rose tint; 
this tinge, however, undergoes various modifications, such 
as scarlet, red, rose, yellowish-red, and reddish-purple: it is 
also found blue and black. Its fracture is flattish-conchoidal, 
with a splendent vitreous lustre. It occurs crystallised in 
regular octahedrons, sometimes having their edges replaced 
as in macles ; sometimes it assumes the globular form. The 
ruby may be distinguished from the red sapphire and the 
garnet by hardness and specific gravity ; and from reddish 
topaz, which possesses nearly the same specific gravity, by 
its electric properties. 

Composition of red ruby :— 


Silica..2-02 

Alumina ....... 09-01 

Magnesia.26-21 

Protoxide of iron ..... 0 71 

Oxide of chromium , . . . . I'll 

9900 


Reddish Topaz. — For characteristics, &c., see 4 White 
Topaz.’ 

Red Tourmaline. —For characteristics, &c., see 4 Yellow 
Tourmaline.’ 





GOO 


GEMS AND PRECIOUS STONES 


Comparative Table of the Weights of Red or Rose-coloured 
Stones weighed in Air and Water. 


Weight 
in Air 

Giains 

i 

Weight in Water 

Red 

Sapphire 

Deep 

Garnets 

Rubies 

Smoke or 

Red Topaz 

Red 

Tourmaline 

1 

0-7GG 

0-750 

0-722 

0-716 

0-690 

4 

3'0G0 

3-700 

2-880 

2-860 

2-760 

8 

6*120 

6000 

5-770 

5-720 

5-520 

12 

9180 

9-000 

8-660 

8-585 

8-280 

16 

12-250 

12-000 

11-550 

11-550 

11-040 

20 

15-310 

15-000 

14-440 

14-420 

13-800 

24 

18-370 

18-000 

17-330 

17-280 

16-560 

28 

21-440 

21000 

20-220 

20-150 

19-320 

32 

24-510 

24-000 

23-110 

23-610 

22-080 

3G 

27-570 

27 000 

26-000 

25-880 

24-840 

40 

30-040 

30 000 

28-880 

28-750 

27-600 

44 

33-710 

33 000 

31-770 

31-610 

30-360 

48 

36"7G0 

36-000 

34-660 

34-470 

33-120 

52 

39-820 

39 000 

37-550 

37-340 

35-880 

5G 

42 890 

42-000 

40-440 

40-200 

38-640 

(50 

44-950 

45 000 

43-300 

43060 

41-400 

(54 

49-010 

48-000 

46-220 

45-930 

44-160 

G8 

52-080 

51-000 

49-110 

48-900 

46-920 

72 

55140 

54 000 

51-990 

51-770 

49-680 

7G 

58-210 

57-000 

54-880 

54-630 

62-440 

80 

01-280 

60-000 

57-770 

57-490 

55-200 

84 

G4 340 

63-000 

60-660 

60-350 

57-960 

88 

67410 

66-000 

63-550 

63-220 

60-720 

02 

70-470 

69-000 

66-440 

66-080 

63-480 

9G 

73-540 

72-000 

69-330 

68-940 

66-240 

100 

7G-G00 

75 000 

72-220 

71-800 

G9000 

1 Specific 
j Gravity 

1 

| 4 270 

4000 

3-600 

3-530 

3-220 


BLUE STONES. 

Blue Sapphire. — For characteristics, &c., see 4 White 
Sapphire.’ 

Disthene , Cyanit'e .—Specific gravity, 3*5—3*7 ; hardness, 
5—7. Fine specimens of disthene possess a bright blue 
colour, which passes insensibly into a deep sky blue. Its 
transparency is nearly perfect, and it presents small pearly 
reflections, which add to the beauty of its colour. The 
primary form of its crystals is a doubly oblique prism, and 
they cleave very readily in the direction of their length. It 
can be readily distinguished from the sapphire by its being 
less hard, as also by its specific gravity. Figs. 170, 177, 
and 178, represent some of its crystalline forms. 













































Composition of a specimen from St. Gothard :_ 

Silica.43 0 

Alumina.550 

Oxide of iron.-5 

9S*5 

Blue Topaz. —For characteristics, &c., see 4 White Topaz.’ 
Blue topaz and disthene having the same specific gravity, 
may by that test alone be confounded with each other; but 
the appearance of each is so different, that they can be 
rarely confounded. If, however, the electrical test be 
applied, no fear of mistaking one for the other need be 
entertained, as only the topaz becomes electrical. 

Blue Tourmaline. —For characteristics, &c. see 4 Yellow 
Tourmaline.’ 

Blue Beryl. —For characteristics, &c., see 4 Emerald.’ The 
tint and appearance of this stone and that of the blue topaz 
are so similar that they cannot be distinguished by that test; 
their specific gravities, however, are so different, that they 
may, by this simple means, be readily discriminated. 

Dichroite , Water Sapphire. —Specific gravity, 2-56—2-65 ; 
hardness, 7—7*5. The chief characteristic of this stone is, 
that it possesses a double colour; that is, it is a fine blue 
or a normal yellow, as it is viewed in the direction of its 
base, or the planes of a hexahedral prism, which is its 
crystalline form. It can be thus readily distinguished, as 
also by its having nearly the same specific gravity of quartz, 
and thus being the lightest of the blue stones. Composi¬ 
tion :— 


Y Y 2 














692 


GEMS AND PRECIOUS STONES. 


Silica .... 



. 48-35 

Alumina .... 



. 31-71 

Magnesia .... 



. 10-16 

Protoxide of iron 



. 8-12 

Protoxide of mangnnese 



•33 

Loss in fire (water . 



•60 


91)-27 


Turquoise. — Specific gravity, 2-8—3 ; hardness, 5—G. 
This stone has not been placed in the list of specific gravi¬ 
ties, as it can be so readily detected by its appearance. It 
is bright or greenish-blue in colour ; its aspect is earthy 
or compact. It scratches apatite, and even glass ; but is 
scratched by quartz. It occurs filling fissures, or forming 
concretions in siliceous and argillo-ferruginous rocks. 


Comparative Table of tiie Weights of Blue Stones weighed 

in Ant and Water. 


Weight 



Weight in Water 



in Air 

Grains 

Blue 

Disthene, 

Blue 

Tour- 

Blue 

Dichroite, 

Water 

Sapphire 

Sapphire 

Cyanite 

Topaz 

maline 

Bery 1 

I i 

0-766 

0-717 

0-716 

0-690 

0-633 

0-622 

4 

3-06 

2-87 

2-86 

2-16 

2-53 

2-49 

8 

6-12 

5-74 

5-72 

5-52 

506 

4-98 

12 

918 

8-61 

8-58 

8-28 

7-59 

7-47 

16 

12-25 

11-48 

11-45 

11-04 

10-12 

9 96 

20 

15-31 

14-35 

14-42 

13-80 

12-05 

12-45 

24 

18-37 

17-22 

17-18 

16-56 

15-19 

14-94 

28 

21-44 

2009 

20-05 

19-32 

17-72 

17-43 

32 

24-51 

22-96 

22-91 

20-08 

20-25 

19-92 

36 

27-57 

25-83 

25-78 

24-84 

22-77 

22-41 

40 

30-64 

28-70 

28-65 

27-60 

25-30 

24-90 

44 

33-71 

31-57 

31-51 

30-36 

27-83 

27-39 

48 

36-76 

34-44 

34-37 

33-12 

30-36 

29-88 

52 

39-82 

37-31 

37-24 

35-88 

32-89 

32-37 

56 

42-89 

40-18 

4010 

38-64 

35-43 

34-86 

60 

45-95 

43-05 

42 96 

41-40 

37-94 

37-35 

64 

4901 

45-92 

45-83 

44-16 

40-47 

39-84 

68 

52-08 

48-79 

48-80 

46-92 

43-00 

42-33 

72 

5514 

51-66 

51-67 

49-68 

45-53 

44-82 

76 

58-21 

54-53 

54-53 

52-44 

48-07 

47-31 

80 

61-28 

57-40 

57-49 

55-20 

50-60 

49-80 

84 

64-34 

60-27 

60-25 

57-96 

53-13 

52-29 

88 

67-41 

63-14 

63-12 

60-72 

55-66 

54-78 

92 

70-47 

6601 

65-98 

63-48 

58-19 

57-27 

96 

73-54 

68-88 

68-84 

66-24 

60-72 

59-76 

100 

76-60 

71-75 

71-70 

69-00 

63-25 

62-25 

Specific 

Gravity 

j 4-27 

3-54 

3-53 

3-22 

2-72 

2-65 








































VIOLET STONES. 


Composition : — 

Phosphoric acid 

Alumina 

Silica 

Peroxide of iron . 

Lime . 

Water and fluoric acid 


(393 


17*80 

10-01 

8-90 

36-82 

0-15 

25-95 

99-69 


VIOLET STONES. 

Violet Sapphire .—For characteristics, &c., see 4 White 
Sapphire.’ 


Comparative Table of the Weights of Violet Stones weighed 

in Air and Water. 


Weight in Air 

Grains 


Weight in Water 

0 

Violet Sapphire 

Violet 

Tourmaline 

Amethystine 

Quartz 

(Amethyst) 

1 

0-766 

0-690 

0-611 

4 

3-06 

2-76 

2-42 

8 

612 

5-52 

4-86 

12 

9-18 

8-28 

7-31 

10 

12-25 

11-04 

9-75 

20 

15-31 

13-80 

12-19 

24 

18-37 

16-56 

14-64 

28 

21-44 

19-32 

17-08 

32 

2451 

20-08 

19-53 

30 

27-57 

24-84 

21-98 

40 

30-64 

27-60 

24-43 

44 

33-71 

30-36 

26-88 

48 

36-76 

33-12 

29-32 

52 

39-82 

35-88 

31-77 

56 

42-89 

38-64 

34-21 

GO 

45-95 

41-40 

36-66 

64 

49-01 

4416 

39-11 

68 

5202 

46-92 

41-56 

72 

55-14 

49-68 

44-00 

76 

58-21 

52-44 

46-44 

80 

61-28 

55-20 

48-88 

84 

64-34 

57-96 

51-32 

88 

67-41 

60-72 

53-76 

92 

70-47 

63-48 

56-21 

96 

73-54 

66-24 

58-65 

100 

76-60 

6900 

61-09 

Specific Gravity 

4-27 

3-22 

2-55 


Violet Tourmaline .—For characteristics, &c., see ‘Yellow 
Tourmaline.’ 

Violet Quartz , Amethyst.— For characteristics, &c., see 
‘ White Quartz.’ 



























694 


GEMS AND PRECIOUS STONES. 


GREEN STONES. 

Green Sapphire. —For characteristics, &c., see 4 Yellow 
Emerald.’ , 

Peridot , Crysolite. —Specific gravity, 3*3—3 5 ; hardness, 
G-5—7. This stone has a more or less deep olive or 
yellowish-green colour. It is more generally found in 
rolled grains than in regular prismatic crystals. It is pos¬ 
sessed in a very high degree of double refraction. Figs. 17 9, 
180, 181, and 182, represent some of its crystalline forms. 


Fig. 179. Fig. 180. 



Green Tourmaline. —For characteristics, see 4 Yellow Tour¬ 
maline.’ 

Emerald. —For characteristics see 4 Yellow Emerald.’ 

Aqua-marine. —This stone possesses a very pale green 
tinge. For other characteristics, see 4 Yellow Emerald.’ 

Chrysoprase. —This mineral is a green-coloured quartz, 
and can be readily recognised by referring to the charac¬ 
teristics of quartz. 







CHATOYANT STONES 


695 


Comparative Table of the Weights of Green Stones weighed 

in Air and Water. 


Weight 
in Air 

Grai ns 



Weight in Water. 


♦ 

Green 

Sapphire 

Peridot 

Green 

Tourmaline 

Emerald 

Aqua 

Marine 

Chryso* 

prase 

1 

0-766 

0-708 

0-690 

0 633 

0-633 

0-611 

4 

306 

2-83 

2-76 

2-53 

2-53 

242 

8 

612 

5-66 

5-52 

5-06 

5-06 

4-86 

12 

9-18 

8-49 

8-28 

7 59 

7-59 

7-31 

16 

12-25 

11-32 

11-04 

10-12 

1012 

9-75 

20 

15-31 

14-16 

13-80 

12-65 

12-65 

12-19 

24 

18-37 

16-99 

16-50 

1519 

15-19 

14-64 

28 

21-44 

19-82 

19-32 

17-72 

17-72 

1708 

32 

24-51 

22-65 

22-08 

20-25 

20-25 

19 53 

30 

27-57 

25-48 

24-84 

22-77 

27-77 

21-98 

40 

30-64 

28-32 

27-60 

25-30 

25-30 

24-43 

44 

33-71 

31-15 

30-36 

27-83 

27-83 

36-88 

48 

36-76 

33-98 

3312 

30-36 

30-36 

29-32 

52 

39-82 

36-81 

35-88 

32-89 

32-89 

31-77 

56 

42-89 

39-64 

38-64 

35-43 

35 43 

34-21 

60 

4595 

42-48 

41-40 

37-94 

37-94 

36-66 

64 

4901 

45 31 

44-16 

40-47 

40-47 

39-11 

68 

52-08 

48-14 

46-92 

43-00 

4300 

41-56 

72 

5514 

50-97 

49-68 

45-53 

45-53 

4400 

76 

58-21 

53-80 

52-44 

48-07 

48-07 

46-44 

80 

61-28 

56-64 

55-20 

50-60 

50-60 

48-88 

84 

64-34 

59-47 

57 96 

53-13 

53-13 

51-32 

88 

07-41 

62-30 

60-72 

55-66 

55-66 

53-76 

92 

70-47 

65-13 

63-48 

58-19 

58-19 

56-21 

96 

73-54 

67-96 

66-24 

60-72 

60-72 

58-65 

100 

76-60 

70-80 

6900 

63 25 

63-25 

61-09 

Specific 

Gravity 

| 4-27 

3-42 

3-22 

2-72 

2-72 

2-56 

?-- 


STONES POSSESSING A PLAY OF COLOURS (CHATOYANT). 

In the following list of stones no regard has been paid to 
absolute colours, but only to the play of colours the stones 
exhibit. This play or reflection is of two kinds: in some, 
as the sapphires, it appears as a white star with six rays, on 
a blue, red, or yellow ground ; or on a purple ground in 
the garnet. In others it is but a point or mass of pearly 
light, which sometimes appears to occupy the whole of the 
stone, and varies according to the inclination given to the 
stone. The cymophane, crysolite quartz, Egyptian emerald, 
felspar, and cat’s eye, belong to this class. 

The specific gravities of such stones as the opal, &c., 























G96 


GEMS AND PRECIOUS STONES. 


have not been given, as the appearance sufficiently charac¬ 
terises them. 

Sapphire. —For characteristics, &c., see 4 White Sapphire.’ 

Garnet. —For characteristics, &c., see 4 Vermeil Garnet.’ 

Cymophane .—See 4 Cymophane.’ 

Antique Emerald. —For characteristics, &c., see 4 Yellow 
Emerald.’ 

Quartz. —See 4 White Quartz.’ 

Felspar , Nacreous Felspar , Fish-eye , df&. — Specific 
gravity, 2’3—25 ; hardness, 4'5—5. This species of fel¬ 
spar has a lamellar texture. It will be seen by the lowness 

} 

Fig. 183. Fig. 184. Fig. 185. 




Fig. 186. 



of its specific gravity that it cannot be readily confounded 
with other stones. In appearance its transparency is nebu¬ 
lous, and it presents pearly white reflections, which float 



















CHATOYANT STONES 


697 


about and vacillate in proportion as its position changes. 
The foregoing are some of the forms of felspar ; see figs. 183, 
184, 185, 186, 187, and 188. 

Composition:— 

Potash.5-26 

Silica.52-90 

Lime.25-20 

Water.1(3-00 

Fluoric acid.0-82 

10008 


Comparative Table of tiie Weights of Stones possessing a 
play of Colours (chatoyant). 


f 

Weight in Water 

Weight 
in Air 
Grains 

Sapphires 

Garnets 

Cymophane 

Antique 

Emerald 

Quartz 

Felspar 

1 

0-766 

0-750 

0-738 

0-633 

0-611 

0-592 

4 

3-06 

3-00 

2-95 

2-53 

2-42 

2-37 

8 

6-12 

6-00 

5-90 

5-06 

4-86 

4-74 

12 

9-18 

9 00 

8-85 

7-59 

7-31 

7-11 

1(3 

12-25 

12-00 

11-80 

1012 

9-75 

9-47 

20 

15-31 

1500 

14-75 

12-65 

12-19 

11-84 

24 

18-37 

18-00 

17-70 

15-19 

14-64 

14-20 

28 

21-44 

21-00 

20-65 

17-72 

17-08 

16-57 

82 

24-51 

2400 

23-60 

20-25 

19-53 

18-94 

3(3 

27-57 

27-00 

26-55 

22-77 

21-98 

21*31 

40 

30 64 

3000 

29-50 

25-30 

24-43 

23-68 

41 

33-71 

33-00 

32-46 

27*83 

26-88 

26-05 

48 

36-76 

3600 

35-40 

30-36 

29*32 

28*42 

52 

39-84 

3900 

38-35 

32-89 

31*77 

30*79 

56 

42-89 

42 00 

41-30 

35-43 

34-21 

33*15 

60 

45-95 

45-00 

44-25 

37-94 

36-66 

35*52 

64 

4901 

48-00 

47*20 

40-47 

39*11 

37-88 

68 

5207 

5100 

50-15 

43-00 

41*56 

40-25 

72 

55-14 

5400 

53-10 

45-53 

44 00 

42-62 

76 

58-21 

57-00 

56-05 

48-07 

46-44 

44-99 

80 

61-28 

6000 

59-00 

50-60 

48-88 

47-36 

84 

64*34 

6300 

61-95 

5313 

51*32 

49*73 

88 

67-47 

66-00 

64-90 

55-66 

53-76 

52*10 

92 

70-47 

69-00 

67-85 

58-19 

56-21 

54-47 

?k> 

73-54 

72-00 

70-80 

6072 

58-65 

56-84 

100 

76-60 

75-00 

73-75 

63-25 

61-09 

59*21 

Specific 

Gravity 

} 4-27 

loo 

3-89 

2-72 

2-55 

2-45 




























































































APPENDIX. 


a 


TABLE I. 


Showing the Quantity of Fine Gold in 1 oz. of any Alloy 
to J of a Carat Grain and the Mint Value of 1 oz. of 
each Alloy. 


Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounce 

Sterling Value, 

Per Ounce 

Oz. 

Buts. 

Grs. 

Carats. Grs. 

Eighths. 

£ 

5. 

d. 

1 

0 

0-000 

24 

0 

0 

4 

4 

11-4545 

0 

10 

23-375 

23 

3 

7 

4 

4 

10-1271 

0 

10 

22-750 

23 

3 

6 

4 

4 

8-7997 

0 

10 

22-125 

23 

3 

5 

4 

4 

7-4723 

0 

10 

21-500 

23 

3 

4 

4 

4 

6-1448 

0 

10 

20-875 

23 

3 

3 

4 

4 

4-8174 

0 

10 

20-250 

23 

3 

2 

4 

4 

3-4000 

0 

10 

10-625 

23 

3 

1 

4 

4 

2-1620 

0 

10 

10-000 

23 

3 

0 

4 

4 

0-8352 

0 

10 

18-375 

23 

2 

7 

4 

3 

11-5078 

0 

10 

17-750 

23 

2 

6 

4 

3 

10-1804 

0 

10 

17-125 

23 

2 

5 

4 

3 

8-8520 

0 

10 

16-500 

23 

2 

4 

4 

3 

7-5255 

0 

10 

15-875 • 

23 

2 

3 

4 

3 

6-1981 

0 

10 

15-250 

23 

2 

2 

4 

3 

4-8707 

0 

10 

14-625 

23 

2 

1 

4 

3 

3-5433 

0 

10 

14-000 

23 

2 

0 

4 

3 

2-2150 

0 

10 

13-375 

23 

1 

7 

4 

3 

0-8885 

0 

10 

12-750 

23 

1 

6 

4 

2 

11-5010 

0 

10 

12-125 

23 

1 

5 

4 

2 

10-2330 

0 

10 

11-500 

23 

1 

4 

4 

2 

8-9062 

0 

10 

10-875 

23 

1 

3 

4 

2 

7-5788 

0 

10 

10-250 

23 

1 

2 

4 

' 2 

0-2514 

0 

10 

0-625 

23 

1 

1 

4 

2 

4-9240 

0 

10 

o-ooo 

23 

1 

0 

4 

2 

3-5905 

0 

10 

8-375 

23 

0 

7 

4 

2 

2-2691 

0 

10 

7-750 

23 

0 

6 

4 

2 

0-0417 

0 

10 

7-125 

23 

0 

5 

4 

1 

11-0143 

0 

10 

6-500 

23 

0 

4 

4 

1 

10-2809 

0 

10 

5-875 

23 

0 

3 

4 

1 

8-9595 

0 

10 

5-250 

23 

0 

2 

4 

1 

7-0321 

0 

10 

4-625 

23 

0 

1 

4 

1 

6-3047 

0 

10 

4-000 

23 

0 

0 

4 

1 

4-9772 

0 

10 

3-375 

22 

o 

o 

7 

4 

1 

3-6498 

0 

10 

2-750 

29 

mm 

3 

6 

4 

1 

2-3224 













GOLD-VALUING TABLE. 


Ill 


Fine Gold, 

Per Ounce 

i 

Carat Gold, 

Per Ounce 

Sterling Value, 

Per Ounce 

Oz. Dwts. Grs. 

Carats. Grs. Eighths. 

£ s. cl. 

0 19 2-125 

22 3 5 

4 1 0-9950 

0 19 1-500 

22 3 4 

4 0 11-0070 

0 19 0-875 

22 3 3 

4 0 10-3402 

0 19 0-250 

22 3 2 

4 0 8-0127 

0 18 23-025 

22 3 1 

4 0 7-0854 

0 18 23-000 

22 3 0 

4 0 0-3579 

0 18 22-375 

22 2 7 

4 0 4-0305 

0 18 21-750 

22 2 6 

4 0 3-7031 

0 18 21-125 

22 2 5 

4 0 2-3757 

0 18 20-500 

22 2 4 

4 0 0-0482 

0 18 19-875 

22 2 3 

3 19 11-7208 

0 18 19-250 

22 2 2 

3 19 10-3934 

0 18 18-625 

22 2 1 

3 19 8-0660 

0 18 18-000 

22 2 0 

3 19 7-7380 

0 18 17-375 

22 1 7 

3 19 6-4112 

0 18 10-750 

22 1 6 

3 19 4-0838 

0 18 16-125 

22 1 5 

3 19 3-7563 

0 18 15-500 

22 1 4 

3 19 2-4289 

0 18 14-875 

22 1 3 

3 19 0-1015 

0 18 14-250 

22 1 2 

3 18 11-7741 

0 18 13-625 

22 1 1 

3 18 10-4467 

0 18 13-000 

22 1 0 

3 18 8-1193 

0 18 12-375 

22 0 7 

3 18 7-7919 

0 18 11-750 

22 0 6 

3 18 6-4044 

0 18 11-125 

22 0 5 

3 18 4-1370 

0 18 10-500 

22 0 4 

3 18 3-8096 

0 18 9-875 

22 0 3 

3 18 2-4822 

0 18 9-250 

22 0 2 

3 18 0-1548 

0 18 8-625 

22 0 1 

3 17 11-8274 

0 18 8-000 

22 0 0 

3 17 10-5000 

0 18 7-375 

21 3 7 

3 17 8-1725 

0 18 0-750 

21 3 6 

3 17 7-8451 

0 18 6-125 

21 3 5 

3 17 0-5177 

0 18 5-500 

21 3 4 

8 17 4-1903 

0 18 4-875 

21 3 3 

3 17 3-8629 

0 18 4-250 

21 3 2 

3 17 2-5355 

0 18 3-025 

21 3 1 

3 17 0-2081 

0 18 3-000 

21 3 0 

3 16 11-8806 

0 18 2-375 

21 2 7 

3 10 10-5532 

0 18 1*750 

21 2 0 

3 16 8-2258 

0 18 i-125 

21 2 5 

3 10 7-8984 

o 18 0-500 

21 2 4 

3 16 6-5710 

0 17 23-875 

21 2 3 

3 16 4-2436 

0 ' 17 23-250 

21 2 2 
a 2 

3 16 3-9162 



















IV 


GOLD VALUING TABLE. 


Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounce 

• 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. Grs. 

Carats. Grs. 

Eighths. 

£ 

s. 


0 

17 

22-625 

21 

2 

1 

3 

16 

2-5887 

0 

17 

22-000 

21 

2 

0 

3 

16 

1-2613 

0 

17 

21-375 

21 

1 

7 

3 

15 

11-9339 

0 

17 

20-750 

21 

1 

6 

3 

15 

10-6065 

0 

17 

20-125 

21 

1 

5 

3 

15 

9-2791 

0 

17 

19-500 

21 

1 

4 

3 

15 

7-9517 

0 

17 

18-875 

21 

1 

3 

3 

15 

6-6243 

0 

17 

18-250 

21 

1 

2 

3 

15 

5-2968 

0 

17 

i 7-625 

21 

1 

1 

3 

15 

3-9694 

0 

17 

17-000 

21 

1 

0 

3 

15 

2-6420 

0 

17 

16-375 

21 

0 

7 

3 

15 

1-3146 

0 

17 

15-750 

21 

0 

6 

3 

14 

11-9872 

0 

' 17 

15-125 

21 

0 

5 

3 

14 

10-6598 

0 

17 

14-500 

21 

0 

4 

3 

14 

9-3324 

0 

17 

13-875 

21 

0 

3 

3 

14 

8-0049 

0 

17 

13-250 

21 

0 

2 

3 

14 

6-6775 

0 

17 

12-625 

21 

0 

1 

3 

14 

5-3501 

0 

17 

12-000 

21 

0 

0 

3 

14 

4-0227 

0 

17 

11-375 

20 

3 

7 

o 

O 

14 

2-6953 

0 

17 

10-750 

20 

3 

6 

3 

14 

1-3678 

0 

17 

10-125 

20 

3 

5 

3 

14 

0-0404 

0 

17 

9-500 

20 

3 

4 

3 

13 

10-7130 

0 

17 

8-875 

20 

3 

3 

3 

13 

9-3856 

0 

17 

8-250 

20 

Q 

o 

2 

3 

13 

8-0582 

0 

17 

7-625 

20 

3 

1 

3 

13 

6-7308 

0 

17 

7-000 

20 

3 

0 

3 

13 

5-4034 

0 

17 

6-375 

20 

2 

7 

3 

13 

4-0759 

0 

17 

5-750 

20 

2 

6 

3 

13 

2-7485 

0 

17 

5-125 

20 

2 

5 

O 

O 

13 

1-4211 

0 

17 

4-500 

20 

2 

4 

3 

13 

0-0937 

0 

17 

3-875 

20 

2 

3 

3 

12 

10-7663 

0 

17 

3-250 

20 

2 

2 

3 

12 

9-4389 

0 

17 

2-625 

20 

2 

1 

3 

12 

8-1115 

0 

17 

2-000 

20 

2 

0 

3 

12 

6-7840 

0 

17 

1*375 

20 

1 

7 

3 

12 

5-4566 

0 

17 

0-750 

20 

1 

6 

3 

12 

4-1292 

0 

17 

0-125 

20 

1 

5 

3 

12 

2-8018 

0 

16 

23-500 

20 

1 

4 

3 

12 

1-4744 

0 

16 

22-875 

20 

1 

3 

3 

12 

0-1470 

0 

16 

22-250 

20 

1 

2 

3 

11 

10-8196 

0 

16 

21-625 

20 

1 

1 

3 

11 

9-4921 

0 

16 

21-000 

20 

1 

0 

3 

11 

8-1647 

0 

16 

20-375 

20 

0 

7 

3 

11 

6-8373 

0 

16 

19-750 

20 

0 

6 

3 

11 

5-5099 












GOLD-VALUING TABLE. 


V 



Fine Gold, 

Carat Gold, 

Sterling Value, 


Per Ounce 

Per Ounce 


Per Ounce 

Oz. 

Bwts. 

Grs. 

Carats. 

Grs. 

Eighths 

£. 

s. 

d. 

0 

16 

19-125 

20 

0 

5 

3 

11 

4-1825 

0 

16 

18-500 

20 

0 

4 

Q 

o 

11 

2-8551 

0 

16 

17-875 

20 

0 

3 

3 

11 

1-5277 

0 

16 

17-250 

20 

0 

2 

3 

11 

0-2002 

0 

16 

16-625 

20 

0 

1 

3 

10 

10-8728 

0 

16 

16-000 

20 

0 

0 

3 

10 

9-5454 

0 

16 

15-375 

19 

3 

7 

3 

10 

8-2180 

0 

16 

14-750 

19 

3 

6 

3 

10 

6-8906 

0 

16 

14-125 

19 

3 

5 

3 

10 

5-5632 

0 

16 

13-500 

19 

3 

4 

3 

10 

4-2357 

0 

16 

12-875 

19 

3 

3 

3 

10 

2-9083 

0 

16 

12-250 

19 

3 

2 

3 

10 

1-5809 

0 

16 

11-625 

19 

3 

1 

3 

10 

0-2534 

0 

16 

11-000 

19 

3 

0 

3 

9 

10-9260 

0 

16 

10-375 

19 

2 

7 

3 

9 

9-5986 

0 

16 

9-750 

19 

2 

6 

3 

9 

8-2712 

0 

16 

9-125 

19 

2 

5 

3 

9 

6-9437 

0 

16 

8-500 

19 

2 

4 

3 

9 

5-6163 

0 

16 

7-875 

19 

2 

3 

3 

9 

4-2889 

0 

16 

7-250 

19 

2 

2 

3 

9 

2-9615 

0 

16 

6-625 

19 

2 

1 

3 

9 

1-6341 

0 

16 

6-000 

19 

2 

0 

3 

9 

0-3067 

0 

16 

5-375 

19 

1 

7 

3 

8 

10-9793 

0 

16 

4-750 

19 

1 

6 

3 

8 

9-6518 

0 

16 

4-125 

19 

1 

5 

3 

8 

8-3244 

0 

16 

3-500 

19 

1 

4 

o 

O 

8 

6-9970 

0 

16 

2-875 

19 

1 

3 

Q 

O 

8 

5-6696 

0 

16 

2-250 

19 

1 

2 

O 

O 

8 

4-3422 

0 

16 

1-625 

19 

1 

1 

o 

O 

8 

3-0148 

0 

16 

1-000 

19 

1 

0 

3 

8 

1-6874 

0 

16 

0-375 

19 

0 

7 

3 

8 

0-3599 

0 

15 

23-750 

19 

0 

6 

3 

7 

11-0325 

0 

15 

23-125 

19 

0 

5 

3 

7 

9-7051 

0 

15 

22-500 

19 

0 

4 

3 

7 

8-3777 

0 

15 

21-875 

19 

0 

3 

3 

7 

7-0503 

0 

15 

21-250 

19 

0 

2 

3 

7 

5-7229 

0 

15 

20-625 

19 

0 

1 

Q 

O 

7 

4-3955 

0 

15 

20-000 

19 

0 

0 

3 

7 

3-0681 

0 

15 

19-375 

18 

3 

7 

3 

7 

1-7407 

0 

15 

18-750 

18 

3 

6 

3 

7 

0-4133 

0 

15 

18-125 

18 

3 

5 

3 

6 

11-0859 

0 

15 

17-500 

18 

3 

4 

3 

6 

9-7585 

0 

15 

16-875 

18 

Q 

o 

3 

Q 

0 

6 

8-4311 

! 0 

15 

16-250 

18 

o 

O 

o 

LA 

o 

O 

6 

7-1036 














VI 


GOLD-VALUING TABLE. 


Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounco 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. 

Grs. 

Carats. 

Grs. 

Eighths. 

£ 

s. 

d. 

0 

15 

15-625 

18 

3 

1 

3 

6 

5-7762 

0 

15 

15-000 

18 

3 

0 

3 

6 

4-4488 

0 

15 

14-375 

18 

2 

7 

3 

6 

3-1214 

0 

15 

13-750 

18 

2 

6 

3 

6 

1-7940 

0 

15 

13-125 

18 

2 

5 

3 

6 

0-4666 

0 

15 

12-500 

18 

2 

4 

3 

5 

11-1392 

0 

15 

11-875 

18 

2 

3 

3 

5 

9-8117 

0 

15 

11-250 

18 

2 

2 

3 

5 

8-4843 

0 

15 

10-625 

18 

2 

1 

3 

5 

7-1569 

0 

15 

10-000 

18 

2 

0 

3 

5 

5-8295 

0 

15 

9-375 

18 

1 

7 

3 

5 

4-5021 

0 

15 

8-750 

18 

1 

6 

3 

5 

3-1747 

0 

15 

8-125 

18 

1 

5 

3 

5 

1-8473 

0 

15 

7-500 

18 

1 

4 

3 

5 

0-5198 

0 

15 

6-875 

18 

1 

3 

3 

4 

11-1924 

0 

15 

6-250 

18 

1 

2 

3 

4 

9-8650 

0 

15 

5-625 

18 

1 

1 

3 

4 

8-5376 

0 

15 

5-000 

18 

1 

0 

3 

4 

7-2102 

0 

15 

4-375 

18 

0 

7 

3 

4 

5-8828 

0 

15 

3-750 

18 

0 

6 

3 

4 

4-5554 

0 

15 

3-125 

18 

0 

5 

3 

4 

3-2279 

0 

15 

2-500 

18 

0 

4 

3 

4 

1-9005 

0 

15 

1-875 

18 

0 

3 

3 

4 

0-5731 

0 

15 

1-250 

18 

0 

2 

3 

3 

11-2457 

0 

15 

0-625 

18 

0 

1 

3 

3 

9-9183 

0 

15 

0-000 

18 

0 

0 

3 

3 

8-5909 

0 

14 

23-375 

17 

3 

7 

3 

3 

7-2634 

0 

14 

22-750 

17 

3 

6 

3 

3 

5-9360 

0 

14 

22-125 

17 

o 

O 

5 

3 

3 

4-6086 

0 

14 

21-500 

17 

3 

4 

3 

3 

3-2812 

0 

14 

20-875 

17 

3 

3 

3 

3 

1-9538 

0 

14 

20-250 

17 

3 

2 

3 

3 

0-6264 

0 

14 

19-625 

17 

3 

1 

3 

2 

11-2990 

0 

14 

19-000 

17 

3 

0 

3 

2 

9-9715 

0 

14 

18-375 

17 

2 

7 

3 

2 

8-6441 

0 

14 

17-750 

17 

2 

6 

3 

2 

7-3167 

0 

14 

17-125 

17 

2 

5 

3 

2 

5-9893 

0 

14 

16-500 

17 

2 

4 

3 

2 

4-6619 

0 

14 

15-875 

17 

2 

3 

3 

2 

3-3345 

0 

14 

15-250 

17 

2 

2 

3 

2 

2-0071 

0 

14 

14-625 

17 

2 

1 

3 

2 

0-6796 

0 

14 

14-000 

17 

2 

0 

3 

1 

11-3522 

0 

14 

13-375 

17 

1 

7 

Q 

O 

1 

10-0248 

0 

14 

12-750 

17 

1 

6 1 

3 

1 

8-6974 


















GOLD-VALUING TABLE. 


Vll 


Fine Gold, 

Carat Gold, 

Sterling Value, 

Per Ounce 

Per Ounce 

Per Ounce 


Oz. 

Dwts. 

Grs. 

Carats. 

Grs. Eighths. 

£ 

s. 

d. 

0 

14 

12-125 

17 

1 

5 

3 

1 

7-3700 

0 

14 

11-500 

17 

1 

4 

3 

1 

6-0426 

0 

14 

10-875 

17 

1 

3 

3 

1 

4-7152 

0 

14 

10-250 

17 

1 

2 

3 

1 

3-3877 

0 

14 

9-625 

17 

1 

1 

3 

1 

2-0603 

0 

14 

9-000 

17 

1 

0 

3 

1 

0-7329 

0 

14 

8-375 

17 

0 

7 

3 

0 11-4055 

0 

14 

7-750 

17 

0 

6 

3 

0 10-0781 

0 

14 

7-125 

17 

0 

5 

3 

0 

8-7507 

0 

14 

6-500 

17 

0 

4 

3 

0 

7-4233 

0 

14 

5-875 

17 

0 

3 

3 

0 

6-0958 

0 

14 

5-250 

17 

0 

2 

3 

0 

4-7684 

0 

14 

4-625 

17 

0 

1 

3 

0 

3-4410 

0 

14 

4-000 

17 

0 

0 

3 

0 

2-1136 

0 

14 

3-375 

16 

3 

7 

3 

0 

0-7862 

0 

14 

2-750 

16 

3 

6 

2 

19 

11-4588 

0 

14 

2-125 

16 

3 

5 

2 

19 

10-1313 

0 

14 

1-500 

16 

3 

4 

2 

19 

8-8039 

0 

14 

0-875 

16 

o 

O 

3 

2 

19 

7-4765 

0 

14 

0-250 

16 

3 

2 

2 

19 

6-1491 

0 

13 

23-625 

16 

3 

1 

2 

19 

4-8217 

0 

13 

23-000 

16 

3 

0 

2 

19 

3-4943 

0 

13 

22-375 

16 

2 

7 

2 

19 

2-1669 

0 

13 

21-750 

16 

2 

6 

2 

19 

0-8394 

0 

13 

21-125 

16 

2 

5 

2 

18 

11-5120 

0 

13 

20-500 

16 

2 

4 

2 

18 

10-1846 

0 

13 

19-875 

16 

2 

3 

2 

18 

8-8572 

0 

13 

19-250 

16 

2 

2 

2 

18 

7-5298 

0 

13 

184325 

16 

2 

1 

2 

18 

6-2024 

0 

13 

18-000 

16 

2 

0 

2 

18 

4-8750 

0 

13 

17-375 

16 

1 

7 

2 

18 

3-5475 

0 

13 

16-750 

16 

1 

6 

2 

18 

2-2201 

0 

13 

16-125 

16 

1 

5 

2 

18 

0-8927 

0 

13 

15-500 

16 

1 

4 

2 

17 

11-5653 

0 

13 

14-875 

16 

1 

3 

2 

17 

10-2377 

0 

13 

14-250 

16 

1 

2 

2 

17 

8-9103 

0 

13 

13-625 

16 

1 

1 

2 

17 

7-5829 

0 

13 

13-000 

16 

1 

0 

2 

17 

6-2554 

0 

13 

12-375 

16 

0 

7 

2 

17 

4-9280 

0 

13 

11-750 

16 

0 

6 

2 

17 

3-6006 

0 

13 

11-125 

16 

0 

5 

2 

17 

2-2732 

0 

13 

10-500 

16 

0 

4 

2 

17 

0-9458 

0 

13 

9-875 

16 

0 

o 

O 

2 

16 

11-6184 

0 

13 

9-250 

16 

0 

o 

iU 

9 

u 

16 

10-2909 































GOLD-VALUING TABLE. 


Vlll 


Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounce 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. 

Grs. 

Carats. 

Grs. 

Eighths. 

£ 

s. d. 

0 

13 

8*625 

16 

0 

1 

2 

16 8-9635 

0 

13 

8-000 

16 

0 

0 

2 

16 7-6363 

0 

13 

7-375 

15 

3 

7 

2 

16 6-3089 

0 

13 

6-750 

15 

3 

6 

2 

16 4-9815 

0 

13 

6-125 

15 

3 

5 

2 

16 3-6541 

0 

13 

5-500 

15 

3 

4 

2 

16 2-3267 

0 

13 

4.875 

15 

3 

3 

2 

16 0-9992 

0 

13 

4-250 

15 

3 

2 

2 

15 11-6718 

0 

13 

3-625 

15 

3 

1 

2 

15 10-3444 

0 

13 

3-000 

15 

3 

0 

2 

15 9-0170 

0 

13 

2-373 

15 

2 

7 

2 

15 7-6896 

0 

13 

1-750 

15 

2 

6 

2 

15 6-3622 

0 

13 

1-125 

15 

2 

5 

2 

15 5-0348 

0 

13 

0-500 

15 

2 

4 

2 

15 3-7073 

0 

12 

23-875 

15 

2 

3 

2 

15 2-3799 

0 

12 

23-250 

15 

2 

2 

2 

15 1-0525 

0 

12 

22-625 

15 

2 

1 

2 

14 11-7251 

0 

12 

22-000 

15 

2 

0 

2 

14 10-3976 

0 

12 

21-375 

15 

1 

7 

2 

14 9-0702 

0 

12 

20-750 

15 

1 

6 

2 

14 7-7428 

0 

12 

20-125 

15 

1 

5 

2 

14 6-4154 

0 

12 

19-500 

15 

1 

4 

2 

14 5-0880 

0 

12 

18-875 

15 

1 

3 

2 

14 3-7606 

0 

12 

18-250 

15 

1 

2 

2 

14 2-4332 

0 

12 

17-625 

15 

1 

1 

2 

14 1-1057 

0 

12 

17-000 

15 

1 

0 

2 

13 11-7783 

0 

12 

16-375 

15 

0 

7 

2 

13 10-4509 

0 

12 

15-750 

15 

0 

6 

2 

13 9-1235 

0 

12 

15-125 

15 

0 

5 

2 

13 7-7961 

0 

12 

14*500 

15 

0 

4 

2 

13 6-4687 

0 

12 

13-875 

15 

0 

3 

• 2 

13 5-1413 

0 

12 

13-250 

15 

0 

2 

2 

13 3-8138 

0 

12 

12-625 

15 

0 

1 

2 

13 2-4864 

0 

12 

12-000 

15 

0 

0 

2 

13 1-1591 

0 

12 

11-375 

14 

3 

7 

2 

12 11-8316 

0 

12 

10-750 

14 

3 

6 

2 

12 10-5042 

0 

12 

10-125 

14 

3 

5 

2 

12 9-1768 

0 

12 

9-500 

14 

3 

4 

2 

12 7-8494 

0 

12 

8-875 

14 

3 

3 

2 

12 6-5220 

0 

12 

8-250 

14 

3 

2 

2 

12 5-1946 

0 

12 

7-625 

14 

3 

1 

2 

12 3-8671 

0 

12 

7-000 

14 

o 

O 

0 

2 

12 2-5397 

0 

12 

6-375 

14 

2 

7 

2 

12 1-2123 

0 

12 

5-750 

14 

2 

6 

2 

11 11-8849 




















GOLD-VALUING TABLE. 


IX 


Fine Gold, 

Per Ounce 

Carat Gold, 

' Per Ounce 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. 

•* 

Grs. 

Carats. 

Grs. 

Eighths. 

£ s. d. 

\ 0 

12 

5*125 

14 

2 

5 

2 11 10-5575 

0 

12 

4-500 

14 

2 

4 

2 11 9-2301 

0 

12 

3-875 

14 

2 

3 

2 11 7-9027 

0 

12 

3-250 

14 

2 

2 

2 11 6-5752 

0 

12 

2-625 

14 

2 

1 

2 11 5-2478 

0 

12 

2-000 

14 

2 

0 

2 11 3-9204 

0 

12 

1-375 

14 

1 

7 

2 11 2-5930 

0 

12 

0-750 

14 

1 

6 

2 11 1-2656 

0 

12 

0-125 

14 

1 

5 

2 10 11-9382 

0 

11 

23-500 

14 

1 

4 

2 10 10-6107 

0 

11 

22-875 

14 

1 

3 

2 10 9-2833 

0 

- 11 

22-250 

14 

1 

2 

2 10 7-9559 

0 

11 

21-625 

14 

1 

1 

2 10 6-6285 

0 

11 

21-000 

14 

1 

0 

2 10 5-3011 

0 

11 

20-375 

14 

0 

7 

2 10 3-9737 

0 

11 

19-750 

14 

0 

6 

2 10 2-6463 

0 

11 

19-125 

14 

0 

5 

2 10 1-3188 

0 

11 

18-500 

14 

0 

4 

2 9 11-9914 

0 

11 

17-875 

14 

0 

3 

2 9 10-6640 

0 

11 

17-250 

14 

0 

2 

2 9 9-3366 

0 

11 

16-625 

14 

0 

1 

2 9 8-0092 

0 

11 

16-000 

14 

0 

0 

2 9 6-6818 

0 

11 

15-375 

13 

3 

7 

2 9 5-3544 

0 

11 

14-750 

13 

3 

6 

2 9 4-0269 

0 

11 

14-150 

13 

3 

5 

2 9 2-6995 

0 

11 

13-500 

13 

3 

4 

2 9 1-3721 

0 

11 

12-875 

13 

3 

3 

2 9 0-0447 

0 

11 

12*250 

13 

o 

O 

2 

2 8 10-7173 

0 

11 

11-625 

13 

3 

1 

2 8 9-3899 

0 

11 

11-000 

13 

3 

0 

2 8 8-0625 

0 

11 

10-375 

13 

2 

7 

2 8 6-7350 

0 

11 

9-750 

13 

2 

6 

2 8 5-4076 

0 

11 

9*125 

13 

2 

5 

2 8 4-0802 

0 

11 

8-500 

13 

2 

4 

2 8 2-7528 

0 

11 

7-875 

13 

2 

3 

2 8 1-4254 

0 

11 

7-250 

13 

2 

2 

2 8 0-0980 

0 

11 

6-625 

13 

2 

1 

2 7 10-7705 

0 

11 

6-000 

13 

2 

0 

2 7 9-4431 

0 

11 

5-375 

13 

1 

7 

2 7 8-1157 - 

0 

11 

4-750 

13 

1 

6 

2 7 6-7883 

0 

11 

4*125 

13 

1 

5 

2 7 5-4609 

0 

11 

3-500 

13 

1 

4 

2 7 4-1335 

I 0 

11 

2-875 

13 

1 

3 

2 7 2-8061 

0 

11 

2-250 

13 

1 

2 

2 7 1-4786 


b 




























X 


GOLD-VALUING TABLE. 


Fine Gold, 

Per Ounce. 

Carat Gold, 

Per Ounce 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. 

Grs. 

Carats. 

Grs. 

Eighths. 

£ 

s. 

d. 

0 

11 

1-625 

13 

1 

1 

2 

7 

0-1512 

0 

11 

1-000 

13 

1 

0 

2 

6 

10-8238 

0 

11 

0-375 

13 

0 

7 

2 

6 

9-4964 

0 

10 

23-750 

13 

0 

6 

2 

6 

8-1698 

0 

10 

23-125 

13 

0 

5 

2 

6 

6-8416 

0 

10 

22-500 

13 

0 

4 

2 

6 

5-5142 

0 

10 

21-875 

13 

0 

3 

2 

6 

4-1867 

0 

10 

21-250 

13 

0 

2 

2 

6 

2-8593 

0 

10 

20-625 

13 

0 

1 

2 

6 

1-5319 

0 

10 

20-000 

13 

0 

0 

2 

6 

0-2045 

0 

10 

19-375 

12 

3 

7 

2 

5 

10-8771 

0 

10 

18-750 

12 

3 

6 

2 

5 

9-5497 

0 

10 

18-125 

12 

3 

5 

2 

5 

8-2223 

0 

10 

17-500 

12 

3 

4 

2 

5 

6-8948 

0 

10 

16-875 

12 

3 

3 

2 

5 

5-5674 

0 

10 

16-250 

12 

3 

2 

2 

5 

4-2400 

0 

10 

15-625 

12 

3 

1 

2 

5 

2-9126 

0 

10 

15-000 

12 

3 

0 

2 

5 

1-5852 

0 

10 

14-375 

12 

2 

7 

2 

5 

0-2578 

0 

10 

13-750 

12 

2 

6 

2 

4 

10-9303 

0 

10 

13-125 

12 

2 

5 

2 

4 

9-6029 

0 

10 

12-500 

12 

2 

4 

2 

4 

8-2755 

0 

10 

11-875 

12 

2 

3 

2 

4 

6-9481 

0 

10 

11-250 

12 

2 

2 

2 

4 

5-6207 

0 

10 

10-625 

12 

2 

1 

2 

4 

4-2933 

0 

10 

10-000 

12 

2 

0 

2 

4 

2-9659 

0 

10 

9-375 

12 

1 

7 

2 

4 

1-6384 

0 

10 

8-750 

12 

1 

6 

2 

4 

0-3110 

0 

10 

8-125 

12 

1 

5 

2 

3 

10-8366 

0 

10 

7-500 

12 

1 

4 

2 

3 

9-6562 

0 

10 

6-875 

12 

1 

3 

2 

3 

8-3288 

0 

10 

6-250 

12 

1 

2 

2 

3 

7-0014 

0 

10 

5-625 

12 

1 

1 

2 

3 

5-6740 

0 

10 

5-000 

12 

1 

0 

2 

3 

4*3465 

0 

10 

4-375 

12 

0 

7 

2 

3 

3-0191 

0 

10 

3-750 

12 

0 

6 

2 

3 

1-6917 

0 

10 

3-125 

12 

0 

5 

2 

3 

0-3643 

0 

10 

2-500 

12 

0 

4 

2 

2 

11-0369 

0 

10 

1-875 

12 

0 

3 

2 

2 

9-7095 

0 

10 

1-250 

12 

0 

2 

2 

2 

8-3821 

0 

10 

0-625 

12 

0 

1 

2 

2 

7-0546 

0 

10 

o-ooo 

12 

0 

0 

9 

Ui 

2 

5-7272 

0 

9 

23-375 

11 

3 

7 

2 

2 

4-3998 

0 

9 

22-750 

11 

o 

O 

6 

o 

9 

3-0724 






















GOLD-VALUING TABLE. 


XI 


] 

Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounce 

Sterling Yaltje, 

Per Ounce 

Oz. 

Dwts. 

Grs. 

Carats. 

Grs. 

Eighths. 

£ 

s. 

d. 

0 

9 

22-125 

11 

3 

5 

2 

2 

1-7450 

o 

9 

21-500 

11 

3 

4 

2 

2 

0-4176 

0 

9 

21-875 

11 

3 

3 

2 

1 

11-0901 

0 

9 • 

20-250 

11 

3 

2 

2 

1 

9-7627 

0 

9 

19-625 

11 

3 

1 

2 

1 

8-4353 

0 

9 

19-000 

11 

3 

0 

2 

1 

7-1079 

0 

9 

18-375 

11 

2 

7 

2 

1 

5-7805 

0 

9 

17-750 

11 

2 

6 

2 

1 

4-4531 

0 

9 

17-125 

11 

2 

5 

2 

1 

3-1257 

0 

9 

16-500 

11 

2 

4 

2 

1 

1-7982 

0 

9 

15-875 

11 

2 

3 

2 

1 

0-4708 

0 

9 

15-250 

11 

2 

2 

2 

0 

11-1434 

0 

9 

14-625 

11 

2 

1 

2 

0 

9-8160 

0 

9 

14-000 

11 

2 

0 

2 

0 

8-4886 

0 

9 

13-375 

11 

1 

7 

2 

0 

7-1612 

0 

9 

12-750 

11 

1 

6 

2 

0 

5-8338 

0 

9 

12-125 

11 

1 

5 

2 

0 

4-5063 

0 

9 

11-500 

11 

1 

4 

2 

0 

3-1789 

0 

9 

10-875 

11 

1 

3 

2 

0 

1-8515 

0 

9 

10-250 

11 

1 

2 

2 

0 

0-5241 

0 

9 

9-625 

11 

1 

1 

1 

19 

11-1907 

0 

9 

9-000 

11 

1 

0 

1 

19 

9-8693 

0 

9 

8-375 

11 

0 

7 

1 

19 

8-5419 

0 

9 

7-750 

11 

0 

6 

1 

19 

7-2144 

0 

9 

7-125 

11 

0 

5 

1 

19 

5-8870 

0 

9 

0-500 

11 

0 

4 

1 

19 

4-5596 

0 

9 

5-875 

11 

0 

3 

1 

19 

3-2322 

0 

9 

5-250 

11 

0 

2 

1 

19 

1-9048 

0 

9 

4-625 

11 

0 

1 

1 

19 

0-5774 

0 

9 

4-000 

11 

0 

0 

1 

18 

11-2500 

0 

9 

3-375 

10 

3 

7 

1 

18 

9-9225 

0 

9 

2-750 

10 

3 

6 

1 

18 

8-5951 

0 

9 

2-125 

10 

3 

5 

1 

18 

7-2677 

0 

9 

1-500 

10 

3 

4 

1 

18 

5-9403 

0 

9 

0-875 

10 

3 

3 

1 

18 

4-6129 

0 

9 

0-250 

10 

3 

2 

1 

18 

3-2855 

0 

8 

23*625 

10 

3 

1 

1 

18 

1-9580 

0 

8 

23-000 

10 

3 

0 

1 

18 

0-6306 

0 

8 

22-375 

10 

2 

7 

1 

17 

11-3032 

0 

8 

21-750 

10 

2 

6 

1 

17 

9-9758 

0 

8 

21-125 

10 

2 

5 

1 

17 

8-6484 

0 

8 

20-500 

10 

2 

4 

1 

17 

7-3210 

0 

8 

1.9-875 

10 

2 

3 

1 

17 

5-9936 

' 0 

8 

19-250 

10 

0 

Ui 

b 2 

2 

1 

17 

4-6661 




























XU 


GOLD-VALUING TABLE. 


Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounce 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. 

Grs. 

Carats. 

Grs. 

Eighths. 

£ 

s. 

cl. 

0 

8 

18*625 

10 

2 

1 

1 

17 

3-3387 

0 

8 

18-000 

10 

2 

0 

1 

17 

2-0113 

0 

8 

17-375 

10 

1 

7 

1 

17 

0-6839 

0 

8 

16-750 

10 

1 

6 

1 

16 

11-3565 

0 

8 

16-125 

10 

1 

5 

1 

16 

10-0291 

0 

8 

15-500 

10 

1 

4 

1 

16 

8-7017 

0 

8 

14-875 

10 

1 

3 

1 

16 

7-3742 

0 

8 

14-250 

10 

1 

2 

1 

16 

6*0468 

0 

8 

13-625 

10 

1 

1 

1 

16 

4-7194 

0 

8 

13-000 

10 

1 

0 

1 

16 

3-3920 

0 

8 

12-375 

10 

0 

7 

1 

16 

2-0646 

0 

8 

11-750 

10 

0 

6 

1 

16 

0-7372 

0 

8 

11-125 

10 

0 

5 

1 

15 

11-4098 

0 

8 

10-500 

10 

0 

4 

1 

15 

10-0823 

0 

8 

9-875 

10 

0 

3 

1 

15 

8-7549 

0 

8 

9-250 

10 

0 

2 

1 

15 

7-4275 

0 

8 

8-625 

10 

0 

1 

1 

15 

6-1001 

0 

8 

8-000 

10 

0 

0 

1 

15 

4-7728 

0 

8 

7-375 

9 

3 

7 

1 

15 

3-4454 

0 

8 

6-750 

9 

3 

6 

1 

15 

2-1179 

0 

8 

6-125 

9 

3 

5 

1 

15 

0-7905 

0 

8 

5-500 

9 

3 

4 

1 

14 

11-4631 

0 

8 

4-875 

9 

3 

3 

1 

14 

10-1357 

0 

8 

4-250 

9 

3 

2 

1 

14 

8-8083 

0 

8 

3-625 

9 

3 

1 

1 

14 

7-4809 

0 

8 

3-000 

9 

3 

0 

1 

14 

6-1535 

0 

8 

2-375 

9 

2 

7 

1 

14 

4-8260 

0 

8 

1-750 

9 

2 

6 

1 

14 

3-4986 

0 

8 

1-125 

9 

2 

5 

1 

14 

2-1712 

0 

8 

0-500 

9 

2 

4 

1 

14 

0-8438 

0 

7 

23-875 

9 

2 

3 

1 

13 

11-5164 

0 

7 

23-250 

9 

2 

2 

1 

13 

10-1890 

0 

7 

22-625 

9 

2 

1 

1 

13 

8-8616 

0 

7 

22-000 

9 

2 

0 

1 

13 

7-5341 

0 

7 

21-375 

9 

1 

7 

1 

13 

6-2067 

0 

7 

20-750 

9 

1 

6 

1 

13 

4-8793 

0 

7 

20-125 

9 

1 

5 

1 

13 

3-5519 

0 

7 

19-500 

9 

1 

4 

1 

13 

2-2245 

0 

7 

19-875 

9 

1 

3 

1 

13 

0-8971 

0 

7 

18-250 

9 

1 

2 

1 

12 

11-5697 

0 

7 

17-625 

9 

1 

1 

1 

12 

10-2422 

0 

7 

17-000 

9 

1 

0 

1 

12 

8-9168 

0 

7 

16-375 

9 

0 

7 

1 

12 

7-5874 

0 

7 

15-750 j 

9 

0 

6 

1 

12 

6-2600 

















Xlll 


GOLD-VALUING TABLE. 


Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounce 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. 

Grs. 

Carats. 

Grs. 

Eighths. 

5. cL 

0 

7 

15-125 

9 

0 

5 

1 12 4-9326 

0 

7 

14-500 

9 

0 

4 

1 12 3-6052 

0 

7 

13-875 

9 

0 

3 

1 12 2-2778 

0 

7 . 

13-250 

9 

0 

2 

1 12 0-9503 

0 

7 

12-625 

9 

0 

1 

1 11 11-6229 

0 

7 

12-000 

9 

0 

0 

1 11 10-2954 

0 

7 

11-375 

8 

3 

7 

1 11 8-9680 

0 

7 

10-750 

8 

3 

6 

1 11 7-6406 

0 

7 

10-125 

8 

3 

5 

1 11 6-3132 

0 

7 

9-500 

8 

3 

4 

1 11 4-9857 

0 

7 

8-875 

8 

3 

3 

1 11 3-6583 

0 

7 

8-250 

8 

3 

2 

1 11 2-3309 

0 

7 

7*625 

8 

3 

1 

1 11 1-0035 

0 

7 

7-000 

8 

3 

0 

1 10 11-6761 

0 

7 

G-375 

8 

2 

7 

1 10 10-3487 

0 

7 

5-750 

8 

2 

6 

1 10 9-0213 

0 

7 

5-125 

8 

2 

5 

1 10 7-6938 

0 

7 

4-500 

8 

2 

4 

1 10 6-3664 

0 

7 

3-875 

8 

2 

3 

1 10 5-0390 

0 

7 

3-250 

8 

2 

2 

1 10 3-7116 

0 

7 

2*625 

8 

2 

1 

1 10 2-3843 

0 

7 

2-000 

8 

2 

0 

1 10 1-0568 

0 

7 

1-375 

8 

1 

7 

1 9 11-7294 

0 

7 

0-750 

8 

1 

6 

1 9 10-4019 

0 

7 

0-125 

8 

1 

5 

1 9 9-0745 

0 

6 

23-500 

8 

1 

4 

1 9 7-7471 

0 

6 

22-875 

8 

1 

3 

1 9 6-4197 

0 

6 

22-250 

8 

1 

2 

1 9 5-0923 

0 

6 

21-625 

8 

1 

1 

1 9 3-7649 

0 

6 

21-000 

8 

1 

0 

1 9 2-4375 

0 

6 

20-375 

8 

0 

7 

1 9 1-1100 

0 

6 

19-750 

8 

0 

6 

1 8 11-7826 

0 

6 

19-125 

8 

0 

5 

1 8 10-4552 

0 

6 

18-500 

8 

0 

4 

1 8 9-1278 

0 

6 

17-875 

8 

0 

3 

1 8 7-8004 

0 

6 

17-250 

8 

0 

2 

1 8 6-4730 

0 

6 

16-625 

8 

0 

1 

1 8 5-1455 

0 

6 

16-000 

8 

0 

0 

1 8 3-8181 

0 

G 

15-375 

7 

3 

7 

1 8 2-4907 

0 

G 

14-750 

7 

3 

6 

1 8 1-1633 

0 

G 

14-125 

7 

3 

5 

1 7 11-8359 

0 

G 

13-500 

7 

3 

4 

1 7 10-5085 

0 

G 

12-875 

7 

3 

3 

1 7 9-1811 

0 

G 

12-250 

7 

3 

9 

1 7 7-8536 

























XIV 


GOLD-VALUING TABLE. 


Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounce 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. 

Grs. 

Carats. 

Grs. 

Eighths. 

£ 

s. 

d. 

0 

6 

11-625 

7 

3 

1 

1 

7 

6-5262 

0 

6 

11-000 

7 

3 

0 

1 

7 

5-1988 

0 

6 

10-375 

7 

2 

7 

1 

7 

3-8714 

0 

6 

9-750 

7 

2 

6 

1 

7 

2-5440 

0 

6 

9-125 

7 

2 

5 

1 

7 

1-2166 

0 

6 

8-500 

7 

2 

4 

1 

6 

11-8892 

0 

6 

7-875 

7 

2 

3 

1 

6 

10-5617 

0 

(3 

7-250 

7 

2 

2 

1 

6 

9-2343 

0 

0 

6-625 

7 

2 

1 

1 

6 

7-8069 

0 

6 

6-000 

7 

2 

0 

1 

6 

6-5795 

0 

6 

5-375 

7 

1 

7 

1 

6 

5-2521 

0 

6 

4-750 

7 

1 

6 

1 

6 

3-9247 

0 

6 

4-125 

7 

1 

5 

1 

6 

2-5973 

0 

6 

3-500 

7 

1 

4 

1 

6 

1-2698 

0 

6 

2-875 

7 

1 

3 

1 

5 

11-9424 

0 

6 

2-250 

7 

1 

2 

1 

5 

10-6150 

0 

6 

1-625 

7 

1 

1 

1 

5 

9-2876 

0 

6 

1-000 

7 

1 

0 

1 

5 

7-9602 

0 

6 

0-375 

7 

0 

7 

1 

5 

6-6328 

0 

5 

23-750 

7 

0 

6 

1 

5 

5-3054 

0 

5 

23-125 

7 

0 

5 

1 

5 

8-9779 

0 

5 

22-500 

7 

0 

4 

1 

5 

2-6505 

0 

5 

21-875 

7 

0 

3 

1 

5 

1-3231 

0 

5 

21-250 

7 

0 

2 

1 

4 

11-9957 

0 

5 

20-625 

7 

0 

1 

1 

4 

10-6683 

0 

5 

20-000 

7 

0 

0 

1 

4 

9-3409 

0 

5 

19-375 

6 

3 

7 

1 

4 

8-0134 

0 

5 

18-750 

6 

3 

6 

1 

4 

6-6860 

0 

5 

18-125 

6 

3 

5 

1 

4 

5-3586 

0 

5 

17-500 

6 

3 

4 

1 

4 

4-0312 

0 

5 

16-875 

6 

3 

3 

1 

4 

2-7038 

0 

5 

16-250 

6 

3 

2 

1 

4 

1-3764 

0 

5 

15-625 

6 

3 

1 

1 

4 

0-0490 

0 

5 

15-000 

6 

3 

0 

1 

3 

10-7216 

0 

5 

14-375 

6 

2 

7 

1 

3 

9-3941 

0 

5 

13-750 

6 

2 

6 

1 

3 

8-0667 

0 

5 

13-125 

6 

2 

5 

1 

3 

6-7393 

0 

5 ' 

12-500 

6 

2 

4 

1 

3 

5-4119 

0 

5 

11-875 

6 

2 

3 

1 

3 

4-0845 

0 

5 

11-250 

6 

2 

2 

1 

3 

2-7571 

0 

5 

10-625 

6 

2 

1 

1 

3 

1-4297 

0 

5 

10-000 

6 

2 

0 

1 

3 

0-1022 

0 

5 

9-375 

6 

1 

7 

1 

2 

10-7748 

0 

5 

8-750 

6 

1 

6 

1 

o 

Ld 

9-4474 





























GOLD-VALUING TABLE. 


XV 


Fine Gold, 

Per Ounce 

- 

Carat Gold, 

Per Ounce 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. 

Grs. 

Carats. 

Grs. 

Eighths. 

£ 

s. 

d. 

0 

5 

8-125 

6 

1 

5 

1 

2 

8-1200 

0 

5 

7-500 

6 

1 

4 

1 

2 

6-7926 

0 

5 

6-875 

6 

1 

3 

1 

2 

5-4652 

0 

5 

6-250 

6 

1 

2 

1 

2 

4-1377 

0 

5 

5-625 

6 

1 

1 

1 

2 

2-8103 

0 

5 

5-000 

6 

1 

0 

1 

2 

1-4829 

0 

5 

4-375 

6 

0 

7 

1 

2 

0-1555 

0 

5 

3-750 

6 

0 

6 

1 

1 

10-8281 

0 

5 

3-125 

6 

0 

5 

1 

1 

9-5007 

0 

5 

2-500 

6 

0 

4 

1 

1 

8-1733 

0 

5 

1-875 

6 

0 

3 

1 

1 

6-8458 

0 

5 

1-250 

6 

0 

2 

1 

1 

5-5184 

0 

5 

0-625 

6 

0 

1 

1 

1 

4-1910 

0 

5 

o-ooo 

6 

0 

0 

1 

1 

2-8636 

0 

4 

23-375 

5 

3 

7 

1 

1 

1-5362 

0 

4 

22-750 

5 

3 

6 

i 

1 

0-2088 

0 

4 

22-125 

5 

3 

5 

1 

0 

10-8813 

0 

4 

21-500 

5 

3 

4 

1 

0 

9-5539 

0 

4 

20-875 

5 

3 

3 

1 

0 

8-2265 

0 

4 

20-250 

5 

3 

2 

1 

0 

6-8991 

0 

4 

19-625 

5 

3 

1 

1 

0 

5-5717 

0 

4 

19-000 

5 

3 

0 

1 

0 

4-2443 

0 

4 

18-375 

5 

2 

7 

1 

0 

2-9169 

0 

4 

17-750 

5 

2 

6 

1 

0 

1-5894 

0 

4 

17-125 

5 

2 

5 

1 

0 

0-2620 

0 

4 

16-500 

5 

2 

4 

0 

19 

10-9346 

0 

4 

15-875 

5 

2 

3 

0 

19 

9-6072 

0 

4 

15-250 

5 

2 

2 

0 

19 

8-2798 

0 

4 

14-625 

5 

2 

1 

0 

19 

6-9524 

0 

4 

14-000 

5 

2 

0 

0 

19 

5-6250 

0 

4 

13-375 

5 

1 

7 

0 

19 

4-2975 

0 

4 

12-750 

5 

1 

6 

0 

19 

2-9701 

0 

4 

12*125 

5 

1 

5 

0 

19 

1-6427 

0 

4 

11-500 

5 

1 

4 

0 

19 

0-3153 

0 

4 

10-875 

5 

1 

3 

0 

18 

10-9879 

0 

4 

10-250 

5 

1 

2 

0 

18 

9-6605 

0 

4 

9-625 

5 

1 

1 

0 

18 

8-3331 

0 

4 

9-000 

5 

1 

0 

0 

18 

7-0056 

0 

4 

8-375 

Ik' 

O 

0 

7 

0 

18 

5-6782 

0 

4 

7-750 

5 

0 

6 

0 

18 

4-3508 

0 

4 

7-125 

5 

0 

5 

0 

18 

3-0234 

0 

4 

6-500 

5 

0 

4 

0 

18 

1 -6960 

0 

4 

5-875 

O 

0 

3 

0 

18 

0-3686 

0 

4 

5-250 

5 

0 

2 

0 

17 

11-0411 































XVI 


GOLD-VALUING TABLE. 


f 

Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounce 

Sterling Value,. 

Per Ounce 

Oz. 

Dwts. 

Grs. 

Carats. 

Grs. 

Eighths. 

£ s. 

d. 

0 

4 

4-625 

5 

0 

1 

0 17 

9-7137 

0 

4 

4-000 

5 

0 

0 

0 17 

8-3863 

0 

4 

3-375 

4 

3 

7 

0 17 

7-0589 

0 

4 

2-750 

4 

3 

6 

0 17 

5-7315 

0 

4 

2-125 

4 

3 

5 

0 17 

4*4041 

0 

4 

1-500 

4 

3 

4 

0 17 

3-0707 

0 

4 

0-875 

4 

3 

3 

0 17 

1-7492 

0 

4 

0-250 

4 

3 

2 

0 17 

0-4218 

0 

3 

23-625 

4 

3 

1 

0 16 

11-0944 

0 

3 

23-000 

4 

3 

0 

0 16 

9-7670 

0 

3 

22-375 

4 

2 

7 

0 16 

8-4396 

0 

3 

21-750 

4 

2 

6 

0 16 

7-1122 

0 

t> 

O 

21-125 

4 

2 

5 

0 16 

5-7848 

0 

3 

20-500 

4 

2 

4 

0 16 

4-4573 

0 

3 

19-875 

4 

2 

3 

0 16 

3-1299 

0 

3 

19-250 

4 

2 

2 

0 16 

1-8025 

0 

3 

18-625 

4 

2 

1 

0 16 

0-4751 

0 

3 

18-000 

4 

2 

0 

0 15 

11-1477 

0 

3 

17-375 

4 

1 

7 

0 15 

9-8203 

0 

3 

16-750 

4 

1 

6 

0 15 

8-4929 

0 

3 

16-125 

4 

1 

5 

0 15 

7-1655 

0 

3 

15-500 

4 

1 

4 

0 15 

5-8380 

0 

3 

14-875 

4 

1 

3 

0 15 

4-5106 

0 

3 

14-250 

4 

1 

2 

0 15 

3-1832 

0 

3 

13-625 

4 

1 

1 

0 15 

1-8558 

0 

3 

13-000 

4 

1 

0 

0 15 

0-5284 

0 

3 

12-375 

4 

0 

7 

0 14 

11-2009 

0 

3 

11-750 

4 

0 

6 

0 14 

9-8735 

0 

3 

11-125 

4 

0 

5 

0 14 

8-5461 

0 

3 

10-500 

4 

0 

4 

0 14 

7-2187 

0 

3 

9-875 

4 

0 

3 

0 14 

5-8913 

0 

3 

9-250 

4 

0 

2 

0 14 

4-5039 

0 

3 

8-625 

4 

0 

1 

0 14 

3-2365 

0 

3 

8-000 

4 

0 

0 

0 14 

1-9090 

0 

3 

7-375 

3 

3 

7 

0 14 

0-5816 

0 

3 

6-750 

3 

o 

O 

6 

0 13 

11-2542 

0 

3 

6-125 

3 

3 

5 

0 13 

9-9208 

0 

3 

5-500 

3 

o 

O 

4 

0 13 

8-5994 

0 

3 

4-875 

3 

3 

3 

0 13 

7-2720 

0 

3 

4-250 

3 

O 

O 

2 

0 13 

5-9440 

0 

3 

3-625 

o 

O 

3 

1 

0 13 

4-6171 

0 

o 

O 

3-000 

3 

3 

0 

0 13 

3-2897 

0 

3 

2-375 

3 

o 

u 

7 

0 13 

1-9623 

0 

3 

1-750 

3 

2 

6 

l 

0 13 

0-6349 

























GOLD-VALUING TABLE. 


XVII 


Eine Gold, 

Per Ounce 


Oz. Dwts. Grs. 

0 3 1*125 

0 3 0-500 

0 2 23-875 

0 2 . 23-250 

0 2 22-625 

0 2 22-000 

0 2 21-375 

0 2 20-750 

0 2 20-125 

0 2 19-500 

0 2 18-875 

0 2 18-250 

0 2 17-625 

0 2 17-000 

0 2 16-375 

0 2 15-750 

0 2 15-125 

0 2 14-500 

0 2 13-875 

0 2 13-250 

0 2 12-625 

0 2 12-000 

0 2 11-375 

0 2 10-750 

0 2 10-125 

0 2 9*500 

0 2 8-875 

0 2 8-250 

0 2 7-625 

0 2 7-000 

0 2 6-375 

0 2 5-750 

0 2 5-125 

0 2 4*500 

0 2 3-875 

0 2 3-250 

0 2 2*625 

0 2 2-000 

0 2 1*375 

0 2 0-750 

0 2 0-125 

0 1 23-500 

0 1 22-875 

0 1 22-250 


Carat Gold, 

Per Ounce 


Carat. Grs. Eiqhths. 

3 2 5 

3 2 4 

3 2 3 

3 2 2 

3 2 1 

3 2 0 

3 17 

3 16 

3 15 

3 14 

3 13 

3 12 

3 11 

3 10 

3 0 7 

3 0 6 

3 0 5 

3 0 4 

3 0 3 

3 0 2 

3 0 1 

3 0 0 

2 3 7 

2 3 6 

2 3 5 

2 3 4 

2 3 3 

2 3 2 

2 3 1 

2 3 0 

2 2 7 

2 2 6 

2 2 5 

2 2 4 

2 2 3 

2 2 2 

2 2 1 

2 2 0 

2 17 

2 16 

2 15 

2 14 

2 13 

2 12 

c 


Sterling Value, 

Per Ounce 


£ s. d. 

0 12 11-3075 
0 12 9-9801 

0 12 8-6527 

0 12 7-3250 

0 12 5-9978 

0 12 4-6704 
0 12 3-3430 

0 12 2-0156 
0 12 0-6882 
0 11 11-3607 
0 11 10-0333 
0 11 8-7059 

0 11 7-3785 

0 11 6-0511 

0 11 4-7237 

0 11 3-3963 

0 11 2-0688 
0 11 0-7414 

0 10 11-4140 
0 10 10-0866 
0 10 8-7592 

0 10 7-4318 

0 10 6-1044 
0 10 4-7769 

0 10 3-4495 
0 10 2-1221 
0 10 0-7947 
0 9 11-4673 
0 9 10-1399 

0 9 8-8125 

0 9 7-4850 

0 9 6-1576 

0 9 4-8302 

0 9 3-5028 

0 9 2-1754 

0 9 0-8480 

0 8 11-5205 

0 8 10-1931 

0 8 8-8657 
0 8 7-5383 

0 8 6-2109 

0 8 4-8835 

0 8 3-5561 

0 8 2-2286 




















XVI11 


GOLD-VALUING TABLE. 


Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounce 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. 

Grs. 

Carats. 

Grs. Eighths. 

£ 

s. 

d. 

0 

1 

21-625 

2 

1 

1 

0 

8 

0-9012 

0 

1 

21-000 

2 

1 

0 

0 

7 

11-5738 

0 

1 

20-375 

2 

0 

7 

0 

7 

10-2464 

0 

1 

19-750 

2 

0 

6 

0 

7 

8-9190 

o 

1 

19-125 

2 

0 

5 

0 

7 

7-5916 

0 

1 

18-500 

2 

0 

4 

0 

7 

6-2642 

0 

1 

17-875 

2 

0 

3 

0 

7 

4-9367 

0 

1 

17-250 

2 

0 

2 

0 

7 

3-6093 

0 

1 

16-625 

2 

0 

1 

0 

7 

2-2819 

0 

1 

16-000 

2 

0 

0 

0 

7 

0-9545 

0 

1 

15-375 

1 

3 

7 

0 

6 

11-6271 

0 

1 

14-750 

1 

3 

6 

0 

6 

10-2997 

0 

1 

14-125 

1 

3 

5 

0 

6 

8-9723 

0 

1 

13-500 

1 

3 

4 

0 

6 

7-6448 

0 

1 

12-875 

1 

3 

3 

0 

6 

6-3174 

0 

1 

12-250 

1 

3 

2 

0 

6 

4-9900 

0 

1 

11-625 

1 

3 

1 

0 

6 

3-6626 

0 

1 

11-000 

1 

3 

0 

0 

6 

2-3352 

0 

1 

10-375 

1 

2 

7 

0 

6 

1-0078 

0 

1 

9-750 

1 

2 

6 

0 

5 

11-6803 

0 

1 

9-125 

1 

2 

5 

0 

5 

10-3529 

0 

1 

8-500 

1 

2 

4 

0 

5 

9-0255 

0 

1 

7-875 

1 

2 

3 

0 

5 

7*6981 

0 

1 

7-250 

1 

2 

2 

0 

5 

6-3707 

0 

1 

6-625 

1 

2 

1 

0 

5 

5-0433 

0 

1 

6-000 

1 

2 

0 

0 

5 

3-7159 

0 

1 

5-375 

1 

1 

7 

0 

5 

2-3884 

0 

1 

4-750 

1 

1 

6 

0 

5 

1-0610 

0 

1 

4-125 

1 

1 

5 

0 

4 

11-7836 

0 

1 

3-500 

1 

1 

4 

0 

4 

10-4062 

0 

1 

2-875 

1 

1 

3 

0 

4 

9-0788 

0 

1 

2-250 

1 

1 

2 

0 

4 

7-7514 

0 

1 

1-625 

1 

i 

1 

0 

4 

6-4240 

0 

1 

1-000 

1 

1 

0 

0 

4 

5-0965 

0 

1 

0-375 

1 

0 

7 

0 

4 

3-7691 

0 

0 

23-750 

1 

0 

6 

0 

4 

2-4417 

0 

0 

23-125 

1 

0 

5 

0 

4 

1-1143 

0 

0 

22-500 

1 

0 

4 

0 

3 

11-7869 

0 

0 

21-875 

1 

0 

3 

0 

3 

10-4595 

0 

0 

21-250 

1 

0 

2 

0 

3 

9-1321 

0 

0 

20-625 

1 

0 

1 

0 

3 

7-8046 

0 

0 

20-000 

1 

0 

0 

0 

3 

6-4772 

0 

0 

19-375 

0 

3 

7 

0 

3 

5-1498 

0 

0 

18-750 

0 

3 

6 

0 

3 

3-8224 






















GOLD-VALUING TABLE. 


XIX 


Fine Gold, 

Per Ounce 

Carat Gold, 

Per Ounce 

Sterling Value, 

Per Ounce 

Oz. 

Dwts. Grs. 

Carats. 

Grs. 

Eighths. 

£ 

s. 

d. 

0 

0 

18-125 

0 

3 

5 

0 

3 

2-4950 

0 

0 

17-500 

0 

3 

4 

0 

3 

1-1676 

0 

0 

16-875 

0 

3 

3 

0 

2 

11-8401 

0 

0 

16-250 

0 

3 

2 

0 

2 

10-5127 

0 

0 

15-625 

0 

3 

1 

0 

2 

9-1853 

0 

0 

15-000 

0 

3 

0 

0 

2 

7-8579 

0 

0 

14-375 

0 

2 

7 

0 

2 

6-5305 

0 

0 

13-750 

0 

2 

6 

0 

2 

5-2031 

0 

0 

13-125 

0 

2 

5 

0 

2 

3-8757 

0 

0 

12-500 

0 

2 

4 

0 

2 

2-5482 

0 

0 

11-875 

0 

2 

3 

0 

2 

1-2208 

0 

0 

11-250 

0 

2 

2 

0 

1 

11-8934 

0 

0 

10-625 

0 

2 

1 

0 

1 

10-5660 

0 

0 

10-000 

0 

2 

0 

0 

1 

9-2386 

0 

0 

9-375 

0 

1 

7 

0 

1 

7-9112 

0 

0 

8-750 

o 

1 

6 

0 

1 

6-5838 

0 

0 

8-125 

0 

1 

5 

0 

1 

5-2563 

0 

0 

7-500 

0 

1 

4 

0 

1 

3-9289 

0 

0 

6-875 

0 

1 

3 

0 

1 

2-6015 

0 

0 

6-250 

0 

1 

2 

0 

1 

1-2741 

0 

0 

5-625 

0 

1 

1 

0 

0 

11-9467 

0 

0 

5-000 

0 

1 

0 

0 

0 

10-6193 

0 

0 

4-375 

0 

0 

7 

0 

0 

9-2919 

0 

0 

3-750 

0 

0 

6 

0 

0 

7-9644 

0 

0 

3-125 

0 

0 

5 

0 

0 

6-6370 

0 

0 

2-500 

0 

0 

4 

0 

0 

5-3096 

0 

0 

1-875 

0 

0 

3 

0 

0 

3-9822 

0 

0 

1-250 

0 

0 

2 

0 

0 

2-6548 

0 

0 

0-625 

0 

0 

1 

0 

0 

1-3274 




















XX 


GOLD-VALUING TABLES. 


To convert Mint Value into Bank Value when the Standard 
is expressed in Carats, Grains, and Eighths. This can be 
readily accomplished for every report by the following 
Tables :— 


Table A. 


Carats 

Value in Pence 

Carats 

Value in Pence 

1 

•0681 

13 

•8863 

2 

•1363 

14 

•9545 

3 

•2045 

15 

1-0227 

4 

•2727 

16 

1-0909 

5 

•3409 

17 

1-1590 

6 

•4090 

18 

1-2272 

7 

•4772 

19 

1-2954 

8 

•5454 

20 

1-3636 

9 

•6136 

21 

1-4318 

10 

•6818 

22 

1-5000 

11 

•7600 

23 

1-5681 

12 

•8181 

24 

1-6363 


Table B. 


Carat Grains 

Value in Pence 

Carat Grains 

Value in Pence 

1 

•0170 

3 

•0511 

2 

•0340 

4 

•0681 


Table C. 


Eighth Carat 
Grains 

Value in Pence 

Eighth Carat 
Grains 

Value in Pence 

1 

•0021 

5 

•0106 

3 

•0042 

6 

•0127 

3 

•0063 

7 

•0149 

4 

•0085 

8 

•0170 













































GOLD-VALUING TABLE. Xxi 

Table A gives the difference in price between Mint and Bank 
value for each carat np to fine gold ; Table B the same for carat 
grains; and Table C the same for eighths of carat grains. 

Now as the Bank value of gold is £3 17s. 9 d. per oz. standard 
against Mint value of £3 17s. 10^d., it follows by calculation 
that fine gold would fetch, Bank price, only £4 4s. 9'8182cZ., 
instead of £4 4s. lT4545d., as shown by Table I. of Mint 
Values; and the Bank value of 1 oz. of gold, of any standard 
whatever, may be readily ascertained by the above Tables A, 
B, and C, and Table I.—the Tables A, B, and C, giving the 
quantities in pence to be deducted from the corresponding stan¬ 
dard in Table I. Thus, suppose it is necessary to ascertain the 
Bank value of 1 oz. of gold of 14 carats 2 grains 5 eighths fine : 
refer to Table A, at 14 carats is found -9545cZ.; at 2 grains in 
Table B is found -0340cZ. ; and at 5 eighths in Table C -0106cZ. 
Now *9545 +-0340 +*0106 = *9991, which has to be deducted 
from £2 11s. 10-5575<Z. (see Table I.), leaving £2 11s. 9-5564cZ. as 
the Bank value of 1 oz. of gold of the above fineness. 


Table II. 


Table of relative proportions of Fine Gold and Alloy, with 
the respective Mint Values of 1 oz. of each Alloy when the 
Standard is expressed in Thousandths. 


Fine 

Gold 

Axloy 


Value 

Fine 

Gold 

Alloy 


Value 

1000 

•000 

£ 

4 

s . 

4 

d . 

11-4545 

986 

•014 

£ 

4 

s . 

3 

d . 

9*1821 

999 

•001 

4 

4 

10*4350 

985 

•015 

4 

3 

8-1627 

998 

•002 

4 

4 

9-4156 

984 

•016 

4 

3 

7-1432 

997 

•003 

4 

4 

8*3961 

983 

•017 

4 

3 

6-1238 

996 

•004 

4 

4 

7-3767 

982 

•018 

4 

3 

5-1043 

995 

•005 

4 

4 

6-3572 

981 

•019 

4 

3 

4-0849 

994 

•006 

4 

4 

5-3378 

980 

•020 

4 

3 

3-0654 

993 

•007 

4 

4 

4-3183 

979 

•021 

4 

3 

2-0459 

992 

•008 

4 

4 

3*2989 

978 

•022 

4 

3 

1-0265 

991 

•009 

4 

4 

2*2793 

977 

•023 

4 

3 

0-0070 

990 

•010 

4 

4 

1-2600 

976 

•024 

4 

2 

10-9876 

989 

•Oil 

4 

4 

0-2405 

975 

•025 

4 

2 

9-9681 

988 

•012 

4 

3 

11-2210 

974 

•026 

4 

2 

8-9487 

987 

•013 

4 

3 

10-2016 

973 

•027 

4 

2 

7-9292 

























XXII 


GOLD-VALUING TABLE. 


Fine 

Gold 

Alloy 

Value 

Fine 

Gold 

Alloy 

Value 



£ 

s . 

d . 



£ 

s . 

d . 

972 

•028 

4 

2 

6-9098 

929 

•071 

3 

18 

11-0732 

971 

•029 

4 

2 

5*8903 

928 

•072 

3 

18 

10-0538 

970 

•030 

4 

2 

4-8709 

927 

•073 

3 

18 

9-0343 

969 

•031 

4 

2 

3-8504 

926 

•074 

3 

18 

8-0149 

968 

•032 

4 

2 

2-8319 

925 

•075 

3 

18 

6-9954 

967 

•033 

4 

2 

1-8125 

924 

•076 

3 

18 

5-9759 

966 

•034 

4 

2 

0-7930 

923 

•077 

3 

18 

4-9565 

965 

•035 

4 

1 

11-7736 

922 

•078 

3 

18 

3-9370 

964 

•036 

4 

1 

10-7541 

921 

•079 

3 

18 

2-9176 

963 

•037 

4 

1 

9-7347 

920 

•080 

3 

18 

1-8981 

962 

•038 

4 

1 

8-7152 

919 

•081 

o 

O 

18 

0-8787 

961 

•039 

4 

1 

7-6958 

918 

•082 

3 

17 

11-8592 

960 

•040 

4 

1 

6-6763 

917 

•083 

3 

17 

10-8398 

959 

•041 

4 

1 

5-6569 

916* 

•084 

3 

17 

9*8203 

958 

•042 

4 

1 

4-6374 

915 

•085 

3 

17 

8-8009 

957 

•043 

4 

1 

3-6179 

914 

•086 

3 

17 

7-7814 

956 

*044 

4 

1 

2-5985 

1 913 

•087 

3 

17 

6-7619 

955 

•045 

4 

1 

1-5790 

912 

•088 

3 

17 

5-7425 

954 

•046 

4 

1 

0-5596 

911 

•089 

3 

17 

4-7230 

953 

•047 

4 

0 

11-5401 

910 

•090 

3 

17 

3-7036 

952 

•048 

4 

0 

10-5207 

909 

•091 

3 

17 

2-6841 

951 

•049 

4 

0 

9-5012 

908 

•092 

3 

17 

1-6647 

950 

•050 

4 

0 

8-4818 

907 

•093 

3 

17 

0-6452 

949 

•051 

4 

0 

7-4623 

906 

•094 

3 

16 

11-6258 

948 

•052 

4 

0 

6-4429 

905 

•095 

3 

16 

10-6063 

947 

•053 

4 

0 

5-4234 

904 

•096 

3 

16 

9-5869 

946 

•054 

4 

0 

4-4039 

903 

•097 

3 

16 

8-5674 

945 

•055 

4 

0 

3-3835 

902 

•098 

3 

16 

7-5479 

944 

•056 

4 

0 

2-3650 

901 

•099 

3 

16 

6-5285 

943 

•057 

4 

0 

1-3456 

900 

•100 

3 

16 

5-5090 

942 

•058 

4 

0 

0-3261 

899 

•101 

3 

16 

4-4896 

941 

•059 

3 

19 

11-3067 

898 

•102 

3 

16 

3-4701 

940 

•060 

3 

19 

10-2872 

897 

•103 

3 

16 

2-4507 

939 

•061 

3 

19 

9-2678 

896 

•104 

3 

16 

1-4312 

938 

•062 

3 

19 

8-2483 

895 

•105 

3 

16 

0-4118 

937 

•063 

3 

19 

7-2289 

894 

•106 

3 

15 

11-3923 

936 

•064 

3 

19 

6-2094 

893 

•107 

3 

15 

10-3729 

935 

•065 

3 

19 

5-1899 

892 

•108 

3 

15 

9*3534 

934 

•066 

3 

19 

4-1705 

891 

•109 

3 

15 

8-3339 

933 

•067 

3 

19 

3-1510 

890 

•110 

3 

15 

7-3145 

932 

•068 

3 

19 

2-1316 

889 

•111 

3 

15 

6*2950 

931 

•069 

3 

19 

1-1121 

888 

•112 

3 

15 

5-2756 

930 

•070 

3 

19 

0-0927 

887 

•113 

3 

15 

4-2561 


* 916 666 Standard *083-333 £3 17,s. 10*5000(7. 






























XXI11 


GOLD-VALUING TABLE. 


Fine 

Gold 

Alloy 

Value 

Fine 

Gold 

Alloy 

Value 

886 

•114 

£ 8 . 

3 15 

d . 

3-2367 

841 

•159 

£ s . 

3 11 

d . 

5-3612 

885 

•115 

3 15 

2-2172 

840 

•160 

3 11 

4-3418 

884 

•116 

3 15 

1-1978 

839 

•161 

3 11 

3-3223 

883 

•117 

3 15 

0-1783 

838 

•162 

3 11 

2-3029 

882 

•118 

3 14 

11*1589 

837 

•163 

3 11 

1-3834 

881 

•119 

3 14 

10-1394 

836 

•164 

3 11 

0-2639 

880 

•120 

3 14 

9*1199 

835 

•165 

3 10 11-2445 

879 

•121 

3 14 

8-1005 

834 

•166 

3 10 

L0-2250 

878 

•122 

3 14 

7*0810 

833 

•167 

3 10 

9-2056 

877 

•123 

3 14 

6-0616 

832 

•168 

3 10 

8-1861 

876 

•124 

3 14 

5-0421 

831 

•169 

3 10 

7-1667 

875 

•125 

3 14 

4-0227 

830 

•170 

3 10 

6-1472 

874 

•126 

3 14 

3-0032 

829 

•171 

3 10 

5-1278 

873 

•127 

3 14 

1-9838 

828 

•172 

3 10 

4-1083 

872 

•128 

3 14 

0-9643 

827 

•173 

3 10 

3-0889 

871 

•129 

3 13 

11-9449 

826 

•174 

3 10 

2-0694 

870 

•130 

3 13 

10-9254 

825 

•175 

3 10 

1-0499 

869 

•131 

3 13 

9-9059 

824 

•176 

3 10 

0-0305 

868 

•132 

3 13 

8-8865 

823 

•177 

3 9 

11-0110 

867 

•133 

3 13 

7*8670 

822 

•178 

3 9 

9-9916 

866 

•134 

3 13 

6-8476 

821 

•179 

3 9 

8-9721 

865 

•135 

3 13 

5-8281 

820 

•180 

3 9 

7-9527 

864 

•136 

3 13 

4-8087 

819 

•181 

3 9 

6-9332 

863 

•137 

3 13 

3-7892 

818 

•182 

3 9 

5-9138 

862 

•138 

3 13 

2-7698 

817 

•183 

3 9 

4-8943 

861 

•139 

3 13 

1-7503 

816 

•184 

3 9 

3-8749 

860 

•140 

3 13 

0*7309 

815 

•185 

3 9 

2-8554 

| 859 

•141 

3 12 

11-7114 

814 

•186 

3 9 

1-8359 

858 

•142 

3 12 

10-6919 

813 

•187 

3 9 

0-8165 

1 857 

•143 

3 12 

9-6725 

812 

•188 

3 8 

11-7970 

856 

•144 

3 12 

8-6530 

811 

•189 

3 8 

10-7776 

855 

•145 

3 12 

7-6336 

810 

•190 

3 8 

9-7581 

854 

•146 

3 12 

6-6141 

809 

•191 

3 8 

8-7387 

853 

•147 

3 12 

5-5947 

808 

•192 

3 8 

7-7192 

852 

•148 

3 12 

4-5752 

807 

•193 

3 8 

6-6998 

851 

•149 

3 12 

3-5558 

806 

•194 

3 8 

5-6803 

850 

•150 

3 12 

2-5363 

805 

•195 

3 8 

4-6609 

849 

•151 

3 12 

1*5169 

804 

•196 

3 8 

3-6414 

848 

.152 

3 12 

0-4974 

803 

•197 

3 8 

2-6219 

847 

•153 

3 11 

11-4779 

802 

•198 

3 8 

1*6025 

846 

•154 

3 11 

10-4585 

801 

•199 

3 8 

0-5830 

845 

•155 

3 11 

9-4390 

800 

•200 

3 7 

11-5636 

844 

•156 

3 11 

8-4196 

799 

•201 

3 7 

10-5441 

843 

•157 

3 11 

7-4001 

798 

•202 

3 7 

9-5247 

842 

•158 

3 11 

6-3807 

797 

•203 

3 7 

8*5052 























































XXIV 


GOLD-VALUING TABLE. 


Fine 

Gold 

Alloy 


Value 

Fine 
! Gold 

Alloy 


Value 

796 

•204 

£ 

3 

s . 

7 

d . 

7-4858 

751 

•249 

£ 

3 

s . 

3 

d . 

9*6103 

795 

•205 

3 

7 

6-4663 

750 

•250 

3 

3 

8-5909 

794 

•206 

3 

7 

5-4469 

749 

•251 

3 

3 

7-5714 

793 

•207 

3 

7 

4*4274 

748 

•252 

3 

3 

6*5519 

792 

•208 

3 

7 

3-4979 

747 

•253 

3 

3 

5-5325 

791 

•209 

3 

7 

2-3885 

746 

•254 

3 

3 

4-5130 

790 

•210 

3 

7 

1-3690 

745 

•255 

3 

3 

3-4936 

789 

•211 

3 

7 

0*3496 

744 

•256 

3 

3 

2-4741 

788 

•212 

3 

6 

11*3301 

743 

•257 

3 

3 

1-4547 

787 

•213 

3 

6 

10-3107 

742 

•258 

3 

3 

0-4352 

786 

•214 

3 

6 

9-2912 

741 

•259 

3 

2 

11-4158 

785 

•215 

3 

6 

8-2718 

740 

•260 

3 

2 

10-3963 

784 

•216 

3 

6 

7*2523 

739 

•261 

3 

2 

9-3769 

783 

•217 

3 

6 

6-2329 

738 

•262 

3 

2 

8-3574 

782 

•218 

3 

6 

5-2134 

737 

•263 

3 

2 

7-3379 

781 

•219 

3 

6 

4-1939 

736 

•264 

3 

2 

6-3185 

780 

•220 

3 

6 

3-1745 

735 

•265 

3 

2 

5-2990 

779 

•221 

3 

6 

2-1550 

734 

•266 

3 

2 

4-2796 

778 

•222 

3 

6 

1-1356 

733 

•267 

3 

2 

3-2601 

777 

•223 

3 

6 

0-1161 

732 

•268 

3 

2 

2-2407 

776 

•224 

3 

5 

11-0967 

731 

•269 

3 

2 

1-2212 

775 

•225 

3 

5 

10-0772 

730 

•270 

3 

2 

0-2018 

774 

•226 

8 

5 

9-0578 

729 

•271 

3 

1 

11-1823 

773 

•227 

3 

5 

8-0383 

728 

•272 

3 

1 

10-1629 

772 

•228 

3 

5 

7-0189 

727 

•273 

3 

1 

9-1434 

771 

•229 

3 

5 

5*9994 

726 

•274 

3 

1 

8-1239 

770 

•230 

3 

5 

4-9799 

725 

•275 

3 

1 

7-1045 

769 

•231 

3 

5 

3-9605 

724 

•276 

3 

1 

6-0850 

768 

•232 

3 

5 

2-9410 

723 

•277 

3 

1 

5-0656 

767 

•233 

3 

5 

1-9216 

722 

•278 

3 

1 

4-0461 

766 

•234 

3 

5 

0-9021 

721 

•279 

3 

1 

3-0267 

765 

•235 

3 

4 

11-8827 

720 

•280 

3 

1 

2-0072 

764 

•236 

3 

4 

10-8632 

719 

•281 

3 

1 

0-9878 

763 

•237 

3 

4 

9-8438 

718 

•282 

3 

0 

11-9683 

762 

•238 

3 

4 

8-8243 

717 

•283 

3 

0 

10-9489 

761 

•239 

3 

4 

7-8049 

716 

•284 

3 

0 

9-9294 

760 

•240 

3 

4 

6-7854 

715 

•285 

3 

0 

8-9099 

759 

•241 

3 

4 

5-7659 

714 

•286 

3 

0 

7-8905 

758 

•242 

3 

4 

4-7465 

713 

•287 

3 

0 

6-8710 

757 

•243 

3 

4 

3-7270 

712 

•288 

3 

0 

5-8516 

756 

•244 

3 

4 

2-7076 

711 

•289 

3 

0 

4-8321 

755 

•245 

3 

4 

1-6881 

710 

•290 

3 

0 

3-8127 

754 

•246 

3 

4 

0-6687 

709 

•291 

3 

0 

2-7932 

753 

•247 

3 

3 

11-6492 

708 

•292 

3 

0 

1-7738 

752 1 

•248 

3 

3 

10-6298 

707 

•293 

3 

0 

0-7543 















































GOLD-VALUING TABLE. 


XXV 


Fine 

Gold 

Alloy 


Value 

Fine 

Gold 

Alloy 


Value 

706 

•294 

£ 

2 

s. 

19 

d. 

11-7349 

661 

•339 

£ 

2 

s. 

16 

d. 

1-8594 

705 

•295 

2 

19 

10*7154 

660 

•340 

2 

16 

0-8399 

704 

•296 

2 

19 

9-6959 

659 

•341 

2 

15 

11-8205 

703 

•297 

2 

19 

8-6765 

658 

•342 

2 

15 

10-8010 

702 

•298 

2 

19 

7-6570 

657 

•343 

o 

LA 

15 

9*7816 

701 

•299 

2 

19 

6-6376 

656 

•344 

2 

15 

8-7621 

700 

•300 

2 

19 

5*6181 

655 

•345 

2 

15 

7-7427 

699 

•301 

2 

19 

4-5987 

654 

•346 

2 

15 

6-7232 

698 

•302 

2 

19 

3-5792 

653 

•347 

2 

15 

5-7038 

697 

•303 

2 

19 

2-5598 

652 

•348 

2 

15 

4-6843 

696 

•304 

2 

19 

1-5403 

651 

•349 

2 

15 

3-6649 

695 

•305 

2 

19 

0*5209 

650 

•350 

2 

15 

2-6454 

694 

•306 

2 

18 

11*5014 

649 

•351 

2 

15 

1-6259 

693 

•307 

2 

18 

10-4820 

648 

•352 

2 

15 

0-6065 

692 

•308 

2 

18 

9-4625 

647 

•353 

2 

14 

11-5870 

691 

•309 

2 

18 

8-4430 

646 

•354 

2 

14 

10-5676 

690 

•310 

2 

18 

7-4236 

645 

•355 

2 

14 

9-5481 

689 

•311 

2 

18 

6-4041 

644 

•356 

2 

14 

8-5287 

688 

•312 

2 

18 

5-3847 

643 

•357 

2 

14 

7-5092 

687 

•313 

2 

18 

4-3652 

642 

•358 

2 

14 

6-4898 

686 

•314 

2 

18 

3-3458 

641 

•359 

2 

14 

5-4703 

685 

•315 

2 

18 

2-3263 

640 

•360 

2 

14 

4-4509 

684 

•316 

2 

18 

1-3069 

639 

•361 

2 

14 

3*4314 

683 

•317 

3 

18 

0-2874 

638 

•362 

2 

14 

2-4120 

682 

•318 

2 

17 

11-2680 

637 

•363 

2 

14 

1-3925 

681 

•319 

2 

17 

10-2485 

636 

•364 

2 

14 

0-3730 

680 

•320 

2 

17 

9-2290 

635 

•365 

2 

13 

11-3536 

679 

•321 

2 

17 

8-2096 

634 

•366 

2 

13 

10-3341 

678 

•322 

2 

17 

7-1901 

633 

•367 

2 

13 

9-3147 

677 

•323 

2 

17 

6-1707 

632 

•368 

2 

13 

8-2952 

676 

•324 

2 

17 

5-1512 

631 

•369 

2 

13 

7-2758 

675 

•325 

2 

17 

4-1318 

630 

•370 

2 

13 

6-2563 

674 

•326 

2 

17 

3-1123 

629 

•371 

2 

13 

5-2369 

673 

•327 

2 

17 

2-0929 

628 

•372 

2 

13 

4-2174 

672 

•328 

2 

17 

1-0734 

627 

•373 

2 

13 

3-1979 

671 

•329 

2 

17 

0-0540 

626 

•374 

2 

13 

2-1785 

670 

•330 

2 

16 

11-0345 

625 

•375 

2 

13 

1-1590 

669 

•331 

2 

16 

10-0151 

624 

•376 

2 

13 

0-1396 

668 

•332 

LJ 

16 

8-9956 

623 

•377 

2 

12 

11-1201 

667 

•333 

2 

16 

7-9761 

622 

•378 

2 

12 

10-1007 

666 

•334 

2 

16 

6-9567 

621 

•379 

2 

12 

9-0812 

665 

•335 

2 

16 

5-9372 

620 

•380 

2 

12 

8-0618 

664 

•336 

2 

16 

4-9178 

619 

•381 

2 

12 

7-0423 

663 

•337 

2 

16 

3-8983 

618 

•382 

2 

12 

6-0229 

662 

•338 

2 

16 

2-8789 1 

617 

•383 

2 

12 

5-0034 


d 









































XXVI 


GOLD-VALUING TABLE. 


Fine 

Gold 

Alloy 


Value 

Fine 

Gold 

Alloy 


Value 

616 

•384 

£ 

2 

5. 

12 

d . 

3-9839 

' 

571 

•429 

£ 

2 

5. 

8 

d . 

6-1085 

615 

•385 

2 

12 

2-9645 

570 

•430 

2 

8 

5-0890 

614 

•386 

2 

12 

1-9451 

569 

•431 

2 

8 

4-0696 

613 

•387 

2 

12 

0-9256 

568 

•432 

2 

8 

3-0501 

612 

•388 

2 

11 

11-9061 

567 

•433 

2 

8 

2-0307 

611 

•389 

2 

11 

10-8867 

566 

•434 

2 

8 

1-0112 

610 

•390 

2 

11 

9-8672 

565 

•435 

2 

7 

11-9918 

609 

•391 

2 

11 

8-8478 

564 

*436 

2 

7 

10-9723 

608 

•392 

2 

11 

7-8283 

563 

•437 

2 

7 

9-9529 

607 

•393 

2 

11 

6-8089 

562 

•438 

2 

7 

8-9334 

606 

•394 

2 

11 

5-7894 

561 

•439 

2 

7 

7-9140 

605 

•395 

2 

11 

4-7699 

560 

•440 

2 

7 

6-8945 

604 

•396 

2 

11 

3-7505 

559 

•441 

2 

7 

5-8751 

603 

•397 

2 

11 

2-7311 

558 

•442 

2 

7 

4-8556 

602 

•398 

2 

11 

1-7116 

557 

•443 

2 

7 

3-8361 

601 

•399 

2 

11 

0-6921 

556 

•444 

2 

7 

2-8167 

600 

•400 

2 

10 

11-6727 

555 

•445 

2 

7 

1*7972 

599 

•401 

2 

10 

10-6532 

554 

•446 

2 

7 

0-7778 

598 

•402 

2 

10 

9-6338 

553 

•447 

2 

6 

11-7583 

597 

•403 

2 

10 

8-6143 

552 

•448 

2 

6 

10-7389 

596 

•404 

2 

10 

7-5949 

551 

•449 

2 

6 

9-7194 

595 

•405 

2 

10 

6-5754 

550 

•450 

2 

6 

8-6999 

594 

•406 

2 

10 

5*5559 

549 

•451 

2 

6 

7-6805 

593 

•407 

9 

10 

4*5365 

548 

•452 

2 

6 

6-6611 

592 

•408 

2 

10 

3-5170 

547 

•453 

2 

6 

5-6416 

591 

•409 

2 

10 

2-4976 

546 

•454 

2 

6 

4-6221 

590 

•410 

2 

10 

1-4781 

545 

•455 

2 

6 

3-6027 

589 

•411 

2 

10 

0-4587 

544 

•456 

2 

6 

2-5832 

588 

•412 

2 

9 

11-4392 

543 

•457 

2 

6 

1*5638 

587 

•413 

2 

9 

10-4198 

542 

•458 

2 

6 

0-5443 

586 

•414 

2 

9 

9-4003 

541 

•459 

2 

5 

11-5249 

685 

•415 

2 

9 

8-3809 

540 

•460 

2 

5 

10-5054 

584 

•416 

2 

9 

7-3614 

539 

•461 

2 

5 

9-4859 

583 

•417 

2 

9 

6*3419 

538 

•462 

2 

5 

8-4665 

582 

•418 

2 

9 

5*3225 

537 

•463 

2 

5 

7-4470 

581 

•419 

2 

9 

4-3030 

536 

•464 

2 

5 

6-4276 

580 

•420 

2 

9 

3-2836 

535 

•465 

2 

5 

5-4081 

579 

•421 

2 

9 

2-2641 

534 

•466 

2 

5 

4-3887 

578 

•422 

2 

9 

1-2447 

533 

•467 

2 

5 

3-3692 

577 

•423 

2 

9 

0-2252 

532 

•468 

2 

5 

2-3498 

576 

•424 

2 

8 

11-2058 

531 

•469 

2 

5 

1-3303 

575 

•425 

2 

8 

10-1863 

530 

•470 

2 

5 

0-3109 

574 

•426 

2 

8 

9-1669 

529 

•471 

2 

4 

11-2914 

573 

•427 

2 

8 

8-1474 

528 

•472 

2 

4 

10-2719 

572 

k 

•428 

9 

8 

7-1279 

527 

•473 

2 

4 

9-2525 





















































XXVII 


GOLD-VALUING TABLE. 


Fine 

Gold 

Alloy 


Value 

Fine 

Gold 

Alloy 


Value 

526 

•474 

£ 

2 

s. 

4 

d . 

8*2330 

481 

•519 

£ 

2 

s . 

0 

d . 

10-3576 

525 

•475 

2 

4 

7*2136 

480 

•520 

2 

0 

9-3381 

524 

•476 

2 

4 

6-1941 

479 

•521 

2 

0 

8-3187 

523 

•477 

2 

4 

5-1747 

478 

•522 

2 

0 

7-2992 

522 

•478 

2 

4 

4-1552 

477 

•523 

2 

0 

6-2798 

521 

•479 

2 

4 

3-1358 

476 

•524 

2 

0 

5-2603 

520 

•480 

2 

4 

2*1163 

475 

•525 

2 

0 

4-2409 

519 

•481 

2 

4 

1-0969 

474 

•526 

2 

0 

3-2214 

518 

•482 

2 

4 

0-0774 

473 

•527 

2 

0 

2-2020 

517 

•483 

2 

3 

11-0579 

472 

•528 

2 

0 

1-1825 

516 

•484 

2 

3 

10-0385 

471 

•529 

2 

0 

0-1630 

515 

•485 

2 

3 

9-0190 

470 

•530 

1 

19 

11-1436 

514 

•486 

2 

3 

7-9996 

469 

•531 

1 

19 

10-1241 

513 

•487 

2 

3 

6-9801 

468 

•532 

1 

19 

9-1047 

512 

•488' 

2 

3 

5-9607 

467 

•533 

1 

19 

8-0852 

511 

•489 

2 

3 

4-9412 

466 

•534 

1 

19 

7-0658 

510 

•490 

2 

3 

3-9218 

465 

•535 

1 

19 

6-0463 

509 

•491 

2 

3 

2-9023 

464 

•536 

1 

19 

5-0269 

508 

•492 

2 

3 

1-8829 

463 

•537 

1 

19 

4-0074 

507 

•493 

2 

3 

0-8634 

462 

•538 

1 

19 

2-9879 

506 

•494 

2 

3 

11-8439 

461 

•539 

1 

19 

1-9685 

505 

•495 

2 

2 

10-8245 

460 

•540 

1 

19 

0-9490 

504 

•496 

2 

2 

9-8051 

459 

•541 

1 

18 

11-9296 

503 

•497 

2 

2 

8-7856 

458 

•542 

1 

18 

10-9101 

502 

•498 

2 

2 

7-7661 

457 

•543 

1 

18 

9-8907 

501 

•499 

2 

2 

6-7467 

456 

•544 

1 

18 

8-8712 

500 

•500 

2 

2 

5-7272 

455 

•545 

1 

18 

7-8518 

499 

•501 

2 

2 

4*7078 

454 

•546 

1 

18 

6-8323 

498 

•502 

2 

2 

3-6883 

453 

•547 

1 

18 

5-8129 

497 

•503 

2 

2 

2-6689 

452 

•548 

1 

18 

4-7934 

496 

•504 

2 

2 

1-6494 

451 

•549 

1 

18 

3-7739 

495 

•505 

2 

2 

0-6300 

450 

•550 

1 

18 

2-7545 

494 

•506 

2 

1 

11-6105 

449 

•551 

1 

18 

1-7351 

493 

•507 

2 

1 

10-5911 

448 

•552 

1 

18 

0-7156 

492 

•508 

2 

1 

9-5716 

447 

•553 

1 

17 

11-6961 

491 

•509 

2 

1 

8-5521 

446 

•554 

1 

17 

10-6767 

490 

•510 

2 

1 

7-5327 

445 

•555 

1 

17 

9-6572 

489 

•511 

2 

1 

1-5132 

1 444 

•556 

1 

17 

8-6378 

488 

•512 

2 

1 

5-4938 

443 

•557 

1 

17 

7-6183 

487 

•513 

2 

1 

4-4743 

442 

•558 

1 

17 

6-5989 

486 

•514 

2 

1 

3-4549 

441 

•559 

1 

17 

5-5794 

485 

•515 

2 

1 

2-4354 

440 

•560 

1 

17 

4*5599 

484 

•516 

2 

1 

1-4159 

439 

•561 

1 

17 

3-5405 

483 

•517 

2 

1 

0*3965 

438 

•562 

1 

17 

2-5211 

482 

•518 

2 

0 

11-3770 

1 437 

•563 

1 

17 

1-5016 








































XXV111 GOLD-VALUING TABLE. 


Fixe 

Gold 

Alloy 


Value 

Fine 

Gold 

Alloy 


Value 

436 

•564 

£ 

1 

s. 

17 

d . 

0-4821 

391 

•609 

£ 

1 

s . 

13 

d . 

2-6067 

435 

•565 

1 

16 

11-4627 

390 

•610 

1 

13 

1-5872 

434 

*566 

1 

16 

10-4432 

389 

•611 

1 

13 

0*5678 

433 

•567 

1 

16 

9-4238 

388 

•612 

1 

12 

11-5483 

432 

•568 

1 

16 

8-4043 

387 

•613 

1 

12 

10-5289 

431 

•569 

1 

16 

7*3849 

386 

•614 

1 

12 

9-5094 

430 

•570 

1 

16 

6-3654 

385 

•615 

1 

12 

8-4899 

429 

•571 

1 

16 

5-3459 

384 

•616 

1 

12 

7*4705 

428 

•572 

1 

16 

4*3265 

383 

•617 

1 

12 

6-4511 

427 

•573 

1 

16 

3-3070 

382 

•618 

1 

12 

5*4316 

426 

•574 

1 

16 

2-2876 

381 

•619 

1 

12 

4-4121 

425 

•575 

1 

16 

1-2681 

380 

•620 

1 

12 

3-3927 

424 

•576 

1 

16 

0-2487 

379 

•621 

1 

12 

2-3732 

423 

•577 

1 

15 

11-2292 

378 

•622 

1 

12 

1-3538 

422 

•578 

1 

15 

10-2098 

377 

•623 

1 

12 

0-3343 

421 

•579 

1 

15 

9-1903 

376 

•624 

1 

11 

11-3142 

420 

•580 

1 

15 

8-1709 

375 

•625 

1 

11 

10-2954 

419 

•581 

1 

15 

7-1514 

374 

•626 

1 

11 

9-2759 

418 

•582 

1 

15 

6-1319 

373 

•627 

1 

11 

8*2565 

417 

•583 

1 

15 

5-1125 

372 

•628 

1 

11 

7-2870 

416 

•584 

1 

15 

4-0930 

371 

•629 

1 

11 

6-2176 

415 

•585 

1 

15 

3-0736 

370 

•630 

1 

11 

5-1981 

414 

•586 

1 

15 

2-0541 

369 

•631 

1 

11 

4-1787 

413 

•587 

1 

15 

1-0347 

368 

•632 

1 

11 

3-1592 

412 

•588 

1 

15 

0-0152 

367 

•633 

1 

11 

2-1398 

411 

•589 

1 

14 

10-9958 

366 

•634 

1 

11 

1-1203 

410 

•590 

1 

14 

9*9763 

365 

•635 

1 

11 

0-1009 

409 

•591 

1 

14 

8-9569 

364 

•636 

1 

10 

11-0814 

408 

•592 

1 

14 

7-9374 

363 

•637 

1 

10 

10-0620 

407 

•593 

1 

14 

6-9179 

362 

•638 

1 

10 

9-0425 

406 

•594 

1 

14 

5-8985 

361 

•639 

1 

10 

8-0230 

405 

•595 

1 

14 

4-8790 

360 

•640 

1 

10 

7-0036 

404 

•596 

1 

14 

3*8596 

359 

•641 

1 

10 

5-9841 

403 

•597 

1 

14 

2-8401 

358 

•642 

1 

10 

4-9647 

402 

•598 

1 

14 

1-8207 

357 

•643 

1 

10 

3-9452 

401 

•599 

1 

14 

0-8012 

356 

•644 

1 

10 

2*9258 

400 

•600 

1 

13 

11-7818 

355 

•645 

1 

10 

1-9063 

399 

•601 

1 

13 

10-7623 

354 

•646 

1 

10 

0-8869 

398 

•602 

1 

13 

9-7429 

353 

•647 

1 

9 

11-8674 

397 

•603 

1 

13 

8-7234 

352 

•648 

1 

9 

10-8479 

396 

•604 

1 

13 

7-7039 

351 

•649 

1 

9 

9-8285 

395 

•605 

1 

13 

6-6845 

350 

•650 

1 

9 

8-8090 

394 

•606 

1 

13 

5-6651 

349 

•651 

1 

9 

7-7896 

393 

•607 

1 

13 

4-6456 

348 

•652 

1 

9 

6-7701 

392 

•608 

1 

13 

3-6261 

347 

•653 

1 

9 

5-7507 





































GOLD-VALUING TABLE. 


XXIX 


Fine 

Gold 

Alloy 


Value 

Fine 

Gold 

Alloy 


Value 

346 

•654 

£ 

1 

s . 

9 

d . 

4-7312 

301 

•699 

£ 

1 

s . 

5 

d . 

6-8558 

345 

•655 

1 

9 

3-7118 

300 

•700 

1 

5 

5-8363 

344 

•656 

1 

9 

2*6923 

299 

•701 

1 

5 

4*8169 

343 

•657 

1 

9 

1-6729 

298 

•702 

1 

5 

3*7974 

342 

•658 

1 

9 

0-6534 

297 

•703 

1 

5 

2-7779 

341 

•659 

1 

8 

11-6339 

296 

•704 

1 

5 

1-7585 

340 

•660 

1 

8 

10-6145 

295 

•705 

1 

5 

0-7390 

339 

•661 

1 

8 

9-5951 

294 

•706 

1 

4 

11-7196 

338 

•662 

1 

8 

8-5756 

293 

•707 

1 

4 

10-7011 

337 

•663 

1 

8 

7-5561 

292 

•708 

1 

4 

9*6807 

336 

•664 

1 

8 

6-5367 

291 

•709 

1 

4 

8-6612 

335 

•665 

1 

8 

5-5172 

290 

•710 

1 

4 

7-6418 

334 

•666 

1 

8 

4-4978 

289 

•711 

1 

4 

6-6223 

333 

•667 

1 

8 

3-4783 

288 

•712 

1 

4 

5-6029 

332 

•668 

1 

8 

2-4589 

287 

•713 

1 

4 

4-5834 

331 

•669 

1 

8 

1-4394 

286 

•714 

1 

4 

3-5639 

330 

•670 

1 

8 

0-4199 

285 

•715 

1 

4 

2-5445 

329 

•671 

1 

7 

11-4005 

284 

•716 

1 

4 

1-5251 

328 

•672 

1 

7 

10-3811 

283 

•717 

1 

4 

0-5056 

327 

•673 

1 

7 

9-3616 

282 

•718 

1 

3 

11-4861 

326 

•674 

1 

7 

8-3421 

281 

•719 

1 

3 

10-4667 

325 

•675 

1 

7 

7-3227 

280 

•720 

1 

3 

9-4472 

324 

•676 

1 

7 

6*3032 

279 

•721 

1 

3 

8-4278 

323 

•677 

1 

7 

5-2838 

278 

•722 

1 

3 

7-4083 

322 

•678 

1 

7 

4-2643 

277 

•723 

1 

3 

6-3889 

321 

•679 

1 

7 

3-2449 

276 

•724 

1 

3 

5-3694 

320 

•680 

1 

7 

2-2254 

275 

•725 

1 

3 

4-3499 

319 

•681 

1 

7 

1-2059 

274 

•726 

1 

3 

3-3305 

318 

•682 

1 

7 

0-1865 

273 

•727 

1 

3 

2-3110 

317 

•683 

1 

6 

11-1670 

272 

•728 

1 

3 

1-2916 

316 

•684 

1 

6 

10-1476 

271 

•729 

1 

3 

0-2721 

315 

•685 

1 

6 

9-1281 

270 

•730 

1 

2 

11-2527 

314 

•686 

1 

6 

8-1087 

269 

•731 

1 

2 

10-2332 

313 

•687 

1 

6 

7-0892 

268 

•732 

1 

2 

9-2138 

312 

•688 

1 

6 

6-0698 

267 

•733 

1 

2 

8-1943 

311 

•689 

1 

6 

5-0503 

266 

•234 

1 

2 

7-1749 

310 

•690 

1 

6 

4-0309 

265 

•735 

1 

2 

6-1554 

309 

•691 

1 

6 

3-0114 

264 

•736 

1 

2 

5-1351 

308 

•692 

1 

6 

1-9919 

263 

•737 

1 

2 

4-1165 

307 

•693 

1 

6 

0-9725 

262 

•738 

1 

2 

3-0970 

306 

•694 

1 

5 

11-9530 

261 

•739 

1 

2 

2-0776 

305 

•695 

1 

5 

10-9336 

260 

•740 

1 

2 

1-0581 

304 

•696 

1 

5 

9-9141 

259 

•741 

1 

2 

0-0387 

303 

•697 

1 

5 

8-8947 

258 

•742 

1 

1 

11-0192 

302 

■698 

1 

5 

7-8752 

257 

•743 

1 

1 

9-9998 




























XXX 


GOLD-VALUING TABLE. 


Fine 

Gold 

Alloy 


Value 

Fine 

Gold 

Alloy 


Value 

256 

•744 

£ 

1 

s . 

1 

d . 

8*9803 

211 

•789 

£ 

0 

s . 

17 

d . 

11-1049 

255 

•745 

1 

1 

7-9609 

210 

•790 

0 

17 

10-0854 

254 

•746 

1 

1 

6-9414 

209 

•791 

0 

17 

9-0659 

253 

•747 

1 

1 

5-9219 

208 

•792 

0 

17 

8-0465 

252 

•748 

1 

1 

4-9025 

207 

•793 

0 

17 

7-0270 

251 

•749 

1 

1 

3*8830 

206 

•794 

0 

17 

6-0076 

250 

•650 

1 

1 

2-8636 

205 

•795 

0 

17 

4-9881 

249 

•751 

1 

1 

1-8441 

204 

•796 

0 

17 

3-9687 

248 

•752 

1 

1 

0-8247 

203 

•797 

0 

17 

2-9492 

247 

•753 

1 

0 

11-8052 

202 

•798 

0 

17 

1-9298 

246 

•754 

1 

0 

10-7858 

201 

•799 

0 

17 

0-9103 

245 

•755 

1 

0 

9-7663 

200 

•800 

0 

16 

11-8909 

244 

•756 

1 

0 

8*7469 

199 

•801 

0 

16 

10-8714 

243 

•757 

1 

0 

7-7274 

198 

•802 

0 

16 

9-8519 

242 

•758 

1 

0 

6-7079 

197 

•803 

0 

16 

8-8325 

241 

•759 

1 

0 

5-6885 

196 

•804 

0 

16 

7-8130 

240 

•760 

1 

0 

4-6690 

195 

•805 

0 

16 

6-7936 

239 

•761 

1 

0 

3-6496 

194 

•806 

0 

16 

5-7741 

238 

•762 

1 

0 

2-6301 

193 

•807 

0 

16 

4-7547 

237 

•763 

1 

0 

1-6107 

192 

•808 

0 

16 

3-7352 

236 

•764 

1 

0 

0-5912 

191 

•809 

0 

16 

2-7158 

235 

•765 

0 

19 

11-5718 

190 

•810 

0 

16 

1-6963 

234 

•766 

0 

19 

10-5523 

189 

•811 

0 

16 

0-6769 

233 

•767 

0 

19 

9-5329 

188 

•812 

0 

15 

11-6574 

232 

•768 

0 

19 

8-5134 

187 

•813 

0 

15 

10-6379 

231 

•769 

0 

19 

7-4939 

186 

•814 

0 

15 

9-6185 

230 

•770 

0 

19 

6-4745 

185 

•815 

0 

15 

8-5990 

229 

•771 

0 

19 

5*4551 

184 

•816 

0 

15 

7-5796 

228 

•772 

0 

19 

4-4356 

183 

•817 

0 

15 

6-5601 

227 

•773 

0 

19 

3-4161 

182 

•818 

0 

15 

5-5407 

226 

•774 

0 

19 

2-3967 

181 

•819 

0 

15 

4-5212 

225 

•775 

0 

19 

1-3772 

180 

•820 

0 

15 

3-5018 

224 

•776 

0 

19 

0-3578 

179 

•821 

0 

15 

2-4823 

223 

•777 

0 

18 

11-3383 

178 

•822 

0 

15 

1-4629 

222 

•778 

0 

18 

10-3189 

177 

•823 

0 

15 

0-4434 

221 

•779 

0 

18 

9*2994 

176 

•824 

0 

14 

11-4239 

220 

•780 

0 

18 

8-2799 

175 

•825 

0 

14 

10-4045 

219 

•781 

0 

18 

7-2605 

174 

•826 

0 

14 

9-3851 

218 

•782 

0 

18 

6-2410 

173 

•827 

0 

14 

8-3656 

217 

•783 

0 

18 

5-2216 

172 

•828 

0 

14 

7-3461 

216 

•784 

0 

18 

4-2021 

171 

•829 

0 

14 

6-3267 

215 

•785 

0 

18 

3-1827 

170 

•830 

0 

14 

5-3072 

214 

•786 

0 

18 

2-1632 

169 

•831 

0 

14 

4-2878 

213 

•787 

0 

18 

1-1438 

168 

•832 

0 

14 

3-2683 

212 

•788 

0 

18 

0-1243 

167 

•833 

0 

14 

2-2489 





































GOLD-VALUING TABLE. 


XXXI 


Fine 

Gold 

Alloy 

Value 

Fine 

Gold 

Alloy 


Value 

166 

•834 

£ s . 

0 14 

d . 

1-2294 

121 

•879 

£ s . 

0 10 

d . 

3-3530 

165 

•835 

0 14 

0-2099 

120 

•880 

0 10 

2-3345 

164 

•836 

0 13 11-1905 

119 

•881 

0 10 

1-3151 

163 

•837 

0 13 10-1710 

118 

•882 

0 10 

0-2956 

162 

•838 

0 13 

9-1516 

117 

•883 

0 

9 11-2761 

161 

•839 

0 13 

8-1321 

116 

•884 

0 

9 10-2567 

160 

•840 

0 13 

7-1127 

115 

•885 

0 

9 

9-2372 

159 

•841 

0 13 

6*0932 

114 

•886 

0 

9 

8-2178 

158 

•842 

0 13 

5-0738 

113 

•887 

0 

9 

7-1983 

157 

•843 

0 13 

4-0543 

112 

•888 

0 

9 

6-1789 

156 

•844 

0 13 

3-0349 

111 

•889 

0 

9 

5-1594 

155 

•845 

0 13 

2-0154 

110 

•890 

0 

9 

4-1399 

154 

•846 

0 13 

0-9959 

109 

•891 

0 

9 

3-1205 

153 

•847 

0 12 

11-9765 

108 

•892 

0 

9 

2-1010 

152 

•848 

0 12 

10-9570 

107 

•893 

0 

9 

1-0816 

151 

•849 

0 12 

9-9376 

106 

•894 

0 

9 

0-0621 

150 

•850 

0 12 

8-9181 

105 

•895 

0 

8 

11-0427 

149 

•851 

0 12 

7-8987 

104 

•896 

0 

8 

10-0232 

148 

•852 

0 12 

6-8792 

103 

•897 

0 

8 

9-0038 

147 

•853 

0 12 

5-8598 

102 

•898 

0 

8 

7-9843 

146 

•854 

0 12 

4-8403 

101 

•899 

0 

8 

6-9649 

145 

•855 

0 12 

3*8209 

100 

•900 

0 

8 

5-9454 

144 

•856 

0 12 

2-8014 

99 

•901 

0 

8 

4-9259 

143 

•857 

0 12 

1-7819 

98 

•902 

0 

8 

3-9065 

142 

•858 

0 12 

0-7625 

97 

•903 

0 

8 

2-8870 

141 

•859 

0 11 

11-7430 

96 

•904 

0 

8 

1-8576 

140 

•860 

0 11 

10-7236 

95 

•905 

0 

8 

0-8481 

139 

•861 

0 11 

9-7041 

94 

•906 

0 

7 

11-8287 

138 

•862 

0 11 

8-6847 

93 

•907 

0 

7 

10-8092 

137 

•863 

0 11 

7*6652 

92 

•908 

0 

7 

8-7898 

136 

•864 

0 11 

6-6458 

91 

•909 

0 

7 

9-7703 

135 

•865 

0 11 

5-6263 

90 

•910 

0 

7 

7-7509 

134 

•866 

0 11 

4-6069 

89 

•911 

0 

7 

6-7314 

133 

•867 

0 11 

3-5874 

88 

•912 

0 

7 

5-7119 

132 

•868 

0 11 

2-5679 

87 

•913 

0 

7 

4-6925 

131 

•869 

0 11 

1-5485 

86 

•914 

0 

7 

3-6730 

130 

•870 

0 11 

0-5290 

85 

•915 

0 

7 

2-6536 

129 

•871 

0 10 

11-5096 

84 

•916 

0 

7 

1-6341 

128 

•872 

0 10 

10-4901 

83 

•917 

0 

7 

10-6147 

127 

i -873 

0 10 

9-4707 

82 

•918 

0 

6 

11-5952 

126 

•874 

0 10 

8-4512 

81 

•919 

0 

6 

0-5758 

125 

•875 

0 10 

7-4318 

80 

•920 

0 

6 

9*5563 

124 

1 *876 

0 10 

6-4123 

79 

•921 

0 

6 

8-5369 

123 

•877 

0 10 

5-3929 

78 

•922 

0 

6 

7-5174 

122 

•878 

0 10 

4-3734 

77 

•923 

1 0 

6 

6-4979 



































































XXX11 


GOLD-VALUING TABLE. 


Fine 

Gold 

Alloy 


Value 

Fine 

Gold 

Alloy 


Value 

1 

76 

•924 

£ 

0 

s . 

6 

d . 

5-4785 

38 

•962 

£ 

0 

s . 

3 

d . 

2-7392 

75 

•925 

0 

6 

4-4590 

37 

•963 

0 

3 

1-7198 

74 

•926 

0 

6 

3*4396 

36 

•964 

0 

3 

0-7003 

73 

•927 

0 

6 

2-4201 

35 

•965 

0 

2 

11-6809 

72 

•928 

0 

6 

1-4007 

34 

•966 

0 

2 

10-6614 

71 

•929 

0 

6 

0*3812 

33 

•967 

0 

2 

9-6419 

70 

•930 

0 

5 

11-3618 

32 

•968 

0 

2 

8-6225 

69 

•931 

0 

5 

10-3423 

31 

•969 

0 

2 

7-6030 

68 

•932 

0 

5 

9*3229 

30 

•970 

0 

2 

6-5836 

67 

•933 

0 

5 

8-3034 

29 

•971 

0 

2 

5-5641 

66 

•934 

0 

5 

7-2839 

28 

•972 

0 

2 

4-5447 

65 

•935 

0 

5 

6*2645 

27 

•973 

0 

2 

3-5252 

64 

•936 

0 

5 

5-2451 

26 

•974 

0 

2 

2-5058 

63 

•937 

0 

5 

4-2256 

25 

•975 

0 

2 

1-4863 

62 

•938 

0 

5 

3-2061 

24 

•976 

0 

2 

0-4669 

61 

•939 

0 

5 

2-1867 

23 

•977 

0 

1 

11-4474 

60 

•940 

0 

5 

1-1672 

22 

•978 

0 

1 

10-4279 

59 

•941 

0 

5 

0-1478 

21 

•979 

0 

1 

9-4085 

58 

•942 

0 

4 

11-1283 

20 

•980 

0 

1 

8-3890 

57 

•943 

0 

4 

10-1089 

19 

•981 

0 

1 

7-3696 

56 

•944 

0 

4 

9-0894 

18 

•982 

0 

1 

6-3501 

55 

•945 

0 

4 

8-0699 

17 

•983 

0 

1 

5-3307 

54 

•946 

0 

4 

7-0505 

16 

•984 

0 

1 

4-3112 

53 

•947 

0 

4 

6-0310 

15 

•985 

0 

1 

3-2918 

52 

•948 

0 

4 

5-0116 

14 

•986 

0 

1 

2-2723 

51 

•949 

0 

4 

3-9921 

13 

•987 

0 

1 

1-2529 

50 

•950 

0 

4 

2-9727 

12 

•988 

0 

1 

0-2334 

49 

•951 

0 

4 

1-9532 

11 

•989 

0 

0 

11-2139 

48 

•952 

0 

4 

0-9338 

10 

•990 

0 

0 

10*1945 

47 

•953 

0 

3 

11-9143 

9 

•991 

0 

0 

9-1750 

46 

•954 

0 

3 

10-8949 

'• 8 

•992 

0 

0 

8-1556 

45 

•955 

0 

3 

9-8754 

7 

•993 

0 

0 

7-1361 

44 

•956 

0 

3 

8-8559 

6 

•994 

0 

0 

6-1167 

43 

•957 

0 

3 

7-8365 

5 

•995 

0 

0 

5-0972 

42 

•958 

0 

3 

6-8170 

4 

•996 

0 

0 

4-0778 

41 

•959 

0 

3 

5-7976 

3 

•997 

0 

0 

3-0583 

40 

•960 

0 

3 

4-7781 

2 

•998 

0 

0 

2-0389 

39 

•961 

0 

3 

3-7587 

1 

•999 

0 

0 

1-0194 











































GOLD-VALUING TABLE. 


XXX111 


To convert Mint Value into Bank Value when the Standard 

is expressed in Thousandths. 


Thousandths. 

Value in Pence. 

Thousandths. 

Value in Pence. 

1 

*001636 

6 

•009816 

2 

•003272 

7 

•011352 

3 

•004908 

8 

•013088 

4 

•006544 

9 

•014724 

5 

•008180 




To illustrate the use of the above table, gold of x^oths fine 
may be taken. As in the Table for finding the Bank value of 
gold when the standard is reported in carats, &c., the amounts 
in pence, as above, are to be deducted from the prices attached 
to corresponding standards in Table No. 2. Thus, the minus 
value of -j-^QQ-ths is *00818 of a penny; therefore, the minus value 
0 f _5_Q_[L.th is *818 of a penny, which amount must be deducted 
from the Mint price of gold at the above standard. On refer¬ 
ring to the Table it will be found to be £2 2s. b'7272d. per oz. 
Now, if *818 be deducted, the remainder will be £2 2s. 4*9092^., 
representing the Bank value of 1 oz. of gold of the fineness just 
mentioned. 


e 













XXXIV 


ASSAY TABLE. 


TABLE III. 


Assay Table, showing the Amount of Gold or Silver, in 
Ounces, Pennyweights, and Grains, contained in a Ton of 
Ore, &c. from the Weight of Metal obtained in an Assay 
of 200 Grains of Mineral. 


If 200 Grains of One Ton of Ore 


Ore give of 

will yield of 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

•001 

0 

3 

6 

•002 

0 

6 

12 

•003 

0 

9 

19 

•004 

0 

13 

1 

•005 

0 

16 

8 

•006 

0 

19 

14 

•007 

1 

2 

20 

•008 

1 

6 

3 

•009 

1 

9 

9 

•010 

1 

12 

6 

•011 

1 

15 

22 

•012 

1 

19 

4 

•013 

2 

2 

11 

•014 

2 

5 

17 

•015 

2 

9 

0 

•016 

2 

12 

6 

•017 

2 

15 

12 

•018 

2 

18 

19 

•019 

3 

2 

1 

•020 

3 

5 

8 

•021 

3 

8 

14 

•022 

3 

11 

20 

•023 

3 

15 

3 

•024 

3 

18 

9 

•025 

4 

1 

16 

•026 

4 

4 

22 

•027 

4 

8 

4 

*028 

4 

11 

11 

•029 

4 

14 

17 

•030 

4 

18 

0 


If 200 Grains of 

One Ton of Ore 

Ore give of 

wi 

11 yield of 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

•031 

5 

1 

6 

•032 

5 

4 

12 

•033 

5 

7 

19 

•034 

5 

11 

1 

•035 

5 

14 

8 

•036 

5 

17 

14 

•037 

6 

0 

20 

•038 

6 

4 

3 

•039 

6 

7 

9 

•040 

6 

10 

16 

•041 

6 

13 

22 

•042 

6 

17 

4 

•043 

7 

0 

11 

•044 

7 

3 

17 

•045 

7 

7 

0 

•046 

7 

10 

6 

•047 

7 

13 

12 

•048 

7 

16 

19 

•049 

8 

0 

1 

•050 

8 

3 

8 

•051 

8 

6 

14 

•052 

8 

9 

20 

•053 

8 

13 

3 

•054 

8 

16 

9 

•055 

8 

19 

16 

•056 

9 

2 

22 

•057 

9 

6 

4 

•058 

9 

9 

11 

•059 

9 

12 

17 

•060 

9 

16 

0 







ASSAY TABLE. 


XXXV 


If 200 Grains of One Ton of Ore 

If 200 Grains of One Ton of Ore 

Ure give of 

w 

ill yield of 

Ore give of 

will yield of 

FINE METAL 

FINE METAL 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Diets. Grs. 

Gr. 

Oz. 

Dwts. Grs. 

•061 

9 

19 

6 

•105 

17 

3 

0 

•062 

10 

2 

12 

•106 

17 

6 

6 

•063 

10 

5 

19 

•107 

17 

9 

12 

•064 

10 

9 

1 

•108 

17 

12 

19 

•065 

10 

12 

8 

•109 

17 

16 

1 

•066 

10 

15 

14 

•110 

17 

19 

8 

•067 

10 

18 

20 

•111 

18 

2 

14 

•068 

11 

2 

3 

•112 

18 

5 

20 

•069 

11 

5 

9 

•113 

18 

9 

3 

•070 

11 

8 

16 

•114 

18 

12 

9 

•071 

11 

11 

22 

•115 

18 

15 

16 

•072 

11 

15 

4 

•116 

18 

18 

22 

•073 

11 

18 

11 

•117 

19 

2 

4 

•074 

12 

1 

17 

•118 

19 

5 

11 

•075 

12 

5 

0 

•119 

19 

8 

17 

•076 

12 

8 

6 

•120 

19 

12 

0 

•077 

12 

11 

12 

•121 

19 

15 

6 

•078 

12 

14 

19 

•122 

19 

18 

12 

•079 

12 

18 

1 

•123 

20 

1 

19 

•080 

13 

1 

8 

•124 

20 

5 

1 

•081 

13 

4 

14 

•125 

20 

8 

8 

•082 

13 

7 

20 

•126 

20 

11 

14 

•083 

13 

11 

3 

•127 

20 

14 

20 

•084 

13 

14 

9 

•128 

20 

18 

3 

•085 

13 

17 

16 

•129 

21 

1 

9 

•086 

14 

0 

22 

•130 

21 

4 

16 

•087 

14 

4 

4 

•131 

21 

7 

22 

•088 

14 

7 

11 

•132 

21 

11 

4 

•089 

14 

10 

17 

•133 

21 

14 

11 

•090 

14 

14 

0 

•134 

21 

17 

17 

•091 

14 

17 

6 

•135 

22 

1 

0 

•092 

15 

0 

12 

•136 

22 

4 

6 

•093 

15 

3 

19 

•137 

22 

7 

12 

•094 

15 

7 

1 

•138 

22 

10 

19 

•095 

15 

10 

8 

•139 

22 

14 

1 

•096 

15 

13 

14 

•140 

22 

17 

8 

•097 

15 

16 

20 

•141 

23 

0 

14 

•098 

16 

0 

3 

•142 

23 

3 

20 

•099 

16 

3 

9 

•143 

23 

7 

3 

•100 

16 

6 

16 

•144 

23 

10 

9 

•101 

16 

9 

22 

•145 

23 

13 

16 

•102 

16 

13 

4 

•146 

23 

16 

22 

•103 

16 

16 

11 

•147 

24 

0 

4 

•104 

16 

19 

17 

•148 

24 

3 

11 
















XXXVI 


ASSAY TABLE. 


If 200 grains of 
Ore give of 

One Ton of Ore 
will yield of 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

•149 

24 

6 

17 

•150 

24 

10 

0 

•151 

24 

13 

6 

•152 

24 

16 

12 

•153 

24 

19 

19 

•154 

25 

3 

1 

•155 

25 

6 

8 

•156 

25 

9 

14 

•157 

25 

12 

20 

•158 

25 

16 

3 

•159 

25 

19 

9 

•160 

26 

2 

16 

•161 

26 

5 

22 

•162 

26 

9 

4 

•163 

26 

12 

11 

•164 

26 

15 

17 

•165 

26 

19 

0 

•166 

27 

2 

6 

•167 

27 

5 

12 

•168 

27 

8 

19 

•169 

27 

12 

1 

•170 

27 

15 

8 

•171 

27 

18 

14 

•172 

28 

1 

20 

•173 

28 

5 

3 

•174 

28 

8 

9 

•175 

28 

11 

16 

•176 

28 

14 

22 

•177 

28 

18 

4 

*178 

29 

1 

11 

•179 

29 

4 

17 

•180 

29 

8 

0 

•181 

29 

11 

6 

•182 

29 

14 

12 

•183 

29 

17 

19 

•184 

30 

1 

1 

•185 

30 

4 

8 

•186 

30 

7 

14 

•187 

30 

10 

20 

•188 

30 

14 

3 

•189 

30 

17 

9 

•190 

31 

0 

16 

•191 

31 

3 

22 

•192 

31 

7 

4 


If 200 grains of One Ton of Ore 


Ore give of 

will yield of 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

•193 

31 

10 

11 

•194 

31 

13 

17 

•195 

31 

17 

0 

•196 

32 

0 

6 

•197 

32 

3 

12 

•198 

32 

6 

19 

•199 

32 

10 

1 

•200 

32 

13 

8 

•201 

32 

16 

14 

•202 

32 

19 

20 

•203 

33 

3 

3 

•204 

33 

6 

9 

•205 

33 

9 

16 

•206 

33 

12 

22 

•207 

33 

16 

4 

•208 

33 

19 

11 

•209 

34 

2 

17 

•210 

34 

6 

0 

•211 

34 

9 

6 

•212 

34 

12 

12 

•213 

34 

15 

19 

•214 

34 

19 

1 

•215 

35 

2 

8 

•216 

35 

5 

14 

•217 

35 

8 

20 

•218 

35 

12 

3 

•219 

35 

15 

9 

•220 

35 

18 

16 

•221 

36 

1 

22 

•222 

36 

5 

4 

•223 

36 

8 

11 

•224 

36 

11 

17 

•225 

36 

15 

0 

•226 

36 

18 

6 

•227 

37 

1 

12 

•228 

37 

4 

19 

•229 

37 

8 

1 

•230 

37 

11 

8 

•231 

37 

14 

14 

•232 

37 

17 

20 

•233 

38 

1 

3 

•234 

38 

4 

9 

•235 

38 

7 

16 

•236 

38 

10 

22 














ASSAY TABLE. 


XXXV11 


If 200 Grains of 

Ore give of 

FINK METAL 

Gr. 

•237 

•238 

•239 

•240 

•241 

•242 

•243 

•244 

•245 

•246 

•247 

•248 

•249 

•250 

•251 

•252 

•253 

•254 

•255 

•256 

•257 

•258 

•259 

•260 

•261 

•262 

•263 

•264 

•265 

•266 

•267 

•268 

•269 

•270 

•271 

•272 

•273 

•274 

•275 

•276 

•277 

•278 

•279 

•280 


One Ton of Ore 

will yield of 

FINE METAL 

Oz. 

Diets. 

Grs. 

38 

14 

4 

38 

17 

11 

39 

0 

17 

39 

4 

0 

39 

7 

6 

39 

10 

12 

39 

13 

18 

39 

17 

1 

40 

0 

8 

40 

3 

14 

40 

6 

20 

40 

10 

3 

40 

13 

9 

40 

16 

16 

40 

19 

22 

41 

3 

4 

41 

6 

11 

41 

9 

17 

41 

13 

0 

41 

16 

6 

41 

19 

12 

42 

2 

19 

42 

6 

1 

42 

9 

8 

42 

12 

14 

42 

15 

20 

42 

19 

3 

43 

2 

9 

43 

5 

16 

43 

8 

22 

43 

12 

4 

43 

15 

11 

43 

18 

17 

44 

2 

0 

44 

5 

6 

44 

8 

12 

44 

11 

19 

44 

15 

1 

44 

18 

8 

45 

1 

14 

45 

4 

20 

45 

8 

3 

45 

11 

9 

45 

14 

16 


If 200 Grains of 

Ore give of 

FINE METAL 

Gr. 

•281 

•282 

•283 

•284 

•285 

•286 

•287 

•288 

•289 

•290 

•291 

•292 

•293 

•294 

•295 

•296 

•297 

•298 

•299 

•300 

•301 

•302 

•303 

•304 

•305 

•306 

•307 

•308 

•309 

•310 

•311 

•312 

•313 

*314 

•315 

•316 

•317 

•318 

•319 

•320 

•321 

•322 

•323 

•324 


One Ton of Ore 
will yield of 

FINE METAL 


Oz. 

Dwts. 

Grs. 

45 

17 

22 

46 

1 

4 

46 

4 

11 

46 

7 

17 

46 

11 

0 

46 

14 

6 

46 

17 

12 

47 

0 

19 

47 

4 

1 

47 

7 

8 

47 

10 

14 

47 

13 

20 

47 

17 

3 

48 

0 

9 

48 

3 

16 

48 

6 

22 

48 

10 

4 

48 

13 

11 

48 

16 

17 

49 

0 

0 

49 

3 

6 

49 

6 

12 

49 

9 

19 

49 

13 

1 

49 

16 

8 

49 

19 

14 

50 

2 

20 

50 

6 

3 

50 

9 

9 

50 

12 

16 

50 

15 

22 

50 

19 

4 

51 

2 

11 

51 

5 

17 

51 

9 

0 

51 

12 

6 

51 

15 

12 

51 

18 

19 

52 

2 

1 

52 

5 

8 

52 

8 

14 

52 

11 

20 

52 

15 

3 

52 

18 

9 











XXXV111 


ASSAY TABLE. 


If 200 Grains of One Ton of Ore 

Ore give of will yield of 

FINE METAL FINE METAL 

Gr. 

•325 
•326 
•327 
•328 
•329 
•330 
•331 
•332 
•333 
•334 
•335 
•336 
•337 
•338 
•339 
•340 
•341 
•342 
•343 
•344 
•345 
•346 
•347 
•348 
•349 
•350 
•351 
•352 
•353 
•354 
•355 
•356 
•357 
•358 
•359 
•360 
•361 
•362 
•363 
•364 
•365 
•366 
•367 
•368 


If 200 Grains of 

One Ton of Ore 

Ore give of 

will yield of 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

•369 

60 

5 

9 

•370 

60 

8 

16 

•371 

60 

11 

22 

•372 

60 

15 

4 

•373 

60 

18 

11 

•374 

61 

1 

17 

•375 

61 

5 

0 

•376 

61 

8 

6 

• 377 , 

61 

11 

12 

•378 

61 

14 

19 

•379 

61 

18 

1 

•380 

62 

1 

8 

•381 

62 

4 

14 

•382 

62 

7 

20 

•383 

62 

11 

3 

•384 

62 

14 

9 

•385 

62 

17 

16 

•386 

63 

0 

22 

•387 

63 

4 

4 

•388 

63 

7 

11 

•389 

63 

10 

17 

•390 

63 

14 

0 

•391 

63 

17 

6 

•392 

64 

0 

12 

•393 

64 

3 

19 

•394 

64 

7 

1 

•395 

64 

10 

8 

•396 

64 

13 

14 

•397 

64 

16 

20 

•398 

65 

0 

3 

•399 

65 

3 

9 

•400 

65 

6 

16 

•401 

65 

9 

22 

•402 

65 

13 

4 

•403 

65 

16 

11 

•404 

65 

19 

17 

•405 

66 

3 

0 

•406 

66 

6 

6 

•407 

66 

9 

12 

•408 

66 

12 

19 

•409 

66 

16 

1 

•410 

66 

19 

8 

•411 

67 

2 

14 

•412 

67 

5 

20 


Oz. 

Dwts. 

Grs. 

53 

1 

16 

53 

4 

22 

53 

8 

4 

53 

11 

11 

53 

14 

17 

53 

18 

0 

54 

1 

6 

54 

4 

12 

54 

7 

19 

54 

11 

1 

54 

14 

8 

54 

17 

14 

55 

0 

20 

55 

4 

3 

55 

7 

9 

55 

10 

16 

55 

13 

22 

55 

17 

4 

56 

0 

11 

56 

3 

17 

56 

7 

0 

56 

10 

6 

56 

13 

12 

56 

16 

19 

57 

0 

1 

57 

3 

8 

57 

6 

14 

57 

9 

20 

57 

13 

3 

57 

16 

9 

57 

19 

16 

58 

2 

22 

58 

6 

4 

58 

9 

11 

58 

12 

17 

58 

16 

0 

58 

19 

6 

59 

9 

12 

59 

5 

19 

59 

9 

1 

59 

12 

8 

59 

15 

14 

59 

18 

20 

60 

2 

3 










XXXIX 


ASSAY TABLE. 


If 200 Grains of 

Ore give of 

FINE METAL 

Gr. 

•413 

•414 

•415 

•416 

•417 

•418 

•419 

•420 

•421 

•422 

•423 

•424 

•425 

•426 

•427 

•428 

•429 

•430 

•431 

•432 

•433 

•434 

•435 

•436 

•437 

•438 

•439 

*440 

•441 

•442 

•443 

•444 

•445 

•446 

•447 

•448 

•449 

•450 

•451 

•452 

•453 

•454 

•455 

•456 


One Ton of Ore 
will yield of 


FINE METAL 


Oz. 

Bwts. 

Grs. 

67 

9 

3 

67 

12 

9 

67 

15 

16 

67 

18 

22 

68 

2 

4 

68 

5 

11 

68 

8 

17 

68 

12 

0 

68 

15 

6 

68 

18 

12 

69 

1 

19 

69 

5 

1 

69 

8 

8 

69 

11 

14 

69 

14 

20 

69 

18 

3 

70 

1 

9 

70 

4 

16 

70 

7 

22 

70 

11 

4 

70 

14 

11 

70 

17 

17 

71 

1 

0 

71 

4 

6 

71 

7 

12 

71 

10 

19 

71 

14 

1 

71 

17 

8 

72 

0 

14 

72 

3 

20 

72 

7 

3 

72 

10 

9 

72 

13 

16 

72 

16 

22 

73 

0 

4 

73 

3 

11 

73 

6 

17 

73 

10 

0 

73 

13 

6 

73 

16 

12 

73 

19 

19 

74 

3 

1 

74 

6 

8 

74 

9 

14 


If 200 Grains of 

Ore give of 

FINE METAL 

Gr. 

•457 

•458 

•459 

•460 

•461 

•462 

•463 

•464 

•465 

•466 

•467 

•468 

•469 

•470 

•471 

•472 

•473 

•474 

•475 

•476 

•477 

•478 

•479 

•480 

•481 

•482 

•483 

•484 

•485 

•486 

•487 

•488 

•489 

•490 

•491 

•492 

•493 

•494 

•495 

•496 

•497 

•498 

•499 

•500 


One Ton of Ore 
will yield of 


FINE METAL 


Oz. 

Bwts. 

Grs. 

74 

12 

20 

74 

16 

3 

74 

19 

9 

75 

2 

16 

75 

5 

22 

75 

9 

4 

75 

12 

11 

75 

15 

17 

75 

19 

0 

76 

2 

6 

76 

5 

12 

76 

8 

19 

76 

12 

1 

76 

15 

8 

76 

18 

14 

77 

1 

20 

77 

5 

3 

77 

8 

9 

77 

11 

16 

77 

14 

22 

77 

18 

4 

78 

1 

11 

78 

4 

17 

78 

8 

0 

78 

11 

6 

78 

14 

12 

78 

17 

19 

79 

1 

1 

79 

4 

8 

79 

7 

14 

79 

10 

20 

79 

14 

3 

79 

17 

9 

80 

0 

16 

80 

3 

22 

80 

7 

4 

80 

10 

11 

80 

13 

17 

80 

17 

0 

81 

0 

6 

81 

3 

12 

81 

6 

19 

81 

10 

1 

81 

13 

8 










xl 


ASSAY TABLE. 


If 200 Grains of One Ton of Ore 


Ore give of 

will yield of 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

•501 

81 

16 

14 

•502 

81 

19 

20 

•503 

82 

3 

3 

•504 

82 

6 

9 

•505 

82 

9 

16 

•506 

82 

12 

22 

•507 

82 

16 

4 

•508 

82 

19 

11 

•509 

83 

2 

17 

•510 

83 

6 

0 

•511 

83 

9 

6 

•512 

83 

12 

12 

•513 

83 

15 

19 

•514 

83 

19 

1 

•515 

84 

2 

8 

*516 

84 

5 

14 

•517 

84 

8 

20 

•518 

84 

12 

3 

•519 

84 

15 

9 

•520 

84 

18 

16 

•521 

85 

1 

22 

•522 

85 

5 

4 

•523 

85 

8 

11 

•524 

85 

11 

17 

•525 

85 

15 

0 

•526 

85 

18 

6 

•527 

86 

1 

12 

•528 

86 

4 

19 

•529 

86 

8 

1 

•530 

86 

11 

8 

•531 

86 

14 

14 

•532 

86 

17 

20 

•533 

87 

1 

3 

•534 

87 

4 

9 

•535 

87 

7 

16 

•536 

87 

10 

22 

•537 

87 

14 

4 

•538 

87 

17 

11 

•539 

88 

0 

17 

•540 

88 

4 

0 

•541 

88 

7 

6 

•542 

88 

10 

12 

•543 

88 

13 

19 

*544 

88 

17 

1 


If 200 Grains of 

One Ton of Ore 

Ore give of 

will yield of 

FINfe METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

•545 

89 

0 

8 

•546 

89 

3 

14 

•547 

89 

6 

20 

•548 

89 

10 

3 

•549 

89 

13 

9 

*550 

89 

16 

16 

•551 

89 

19 

22 

•552 

90 

3 

4 

•553 

90 

6 

11 

•554 

90 

9 

17 

•555 

90 

13 

0 

*556 

90 

16 

6 

•557 

90 

19 

12 

•558 

91 

2 

19 

•559 

91 

6 

1 

•560 

91 

9 

8 

•561 

91 

12 

14 

•562 

91 

15 

20 

•563 

91 

19 

3 

•564 

92 

2 

9 

•565 

92 

5 

16 

•566 

92 

8 

22 

•567 

92 

12 

4 

•568 

92 

15 

11 

•569 

92 

18 

17 

•570 

93 

2 

0 

•571 

93 

5 

6 

•572 

93 

8 

12 

•573 

93 

11 

19 

•574 

93 

15 

1 

•575 

93 

18 

8 

•576 

94 

1 

14 

•577 

94 

4 

20 

•578 

94 

8 

3 

•579 

94 

11 

9 

•580 

94 

14 

16 

•581 

94 

17 

22 

•582 

95 

1 

4 

•583 

95 

4 

11 

•584 

95 

7 

17 

•585 

95 

11 

0 

•586 

95 

14 

6 

•587 

95 

17 

12 

•588 

96 

0 

19 
















ASSAY TABLE. 


xli 


If 200 Grains of Ono Ton of Ore 


Ore give of 

will yield of 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

•589 

96 

4 

1 

•590 

96 

7 

8 

•591 

96 

10 

14 

•592 

96 

13 

20 

•593 

96 

17 

3 

•594 

97 

0 

9 

•595 

97 

3 

16 

•596 

97 

6 

22 

•597 

97 

10 

4 

•598 

97 

13 

11 

•599 

97 

16 

17 

•600 

98 

0 

0 

•601 

98 

3 

6 

•602 

98 

6 

12 

•603 

98 

9 

19 

•604 

98 

13 

1 

•605 

98 

16 

8 

•606 

98 

19 

14 

•607 

99 

2 

20 

•608 

99 

6 

3 

•609 

99 

9 

9 

•610 

99 

12 

16 

•611 

99 

15 

22 

•612 

99 

19 

4 

•613 

100 

2 

11 

•614 

100 

5 

17 

•615 

100 

9 

0 

•616 

100 

12 

6 

•617 

100 

15 

12 

•618 

100 

18 

19 

•619 

101 

2 

1 

•620 

101 

5 

8 

•621 

101 

8 

14 

•622 

101 

11 

20 

•623 

101 

15 

3 

•624 

101 

18 

9 

•625 

102 

1 

16 

•626 

102 

4 

22 

•627 

102 

8 

4 

•628 

102 

11 

11 

•629 

102 

14 

17 

•630 

102 

18 

0 

•631 

103 

1 

6 

•632 

103 

4 

12 


If 200 Grains of Ono Ton of Ore 
Ore give of will yield of 

FINE METAL FINE METAL 

Gr. Oz. Dwts. Grs. 

*633 103 7 19 

•634 103 11 1 

•635 103 14 8 

•636 103 17 14 

•637 104 0 20 

•638 104 4 3 

•639 104 7 9 

•640 104 10 16 

•641 104 13 22 

•642 104 17 4 

•643 105 0 11 ' 

•644 105 3 17 

•645 105 7 0 

•646 105 10 6 

•647 105 13 12 

•648 105 16 19 

•649 106 0 1 

•650 106 3 8 

•651 106 6 14 

•652 106 9 20 

•653 106 13 3 

•654 106 16 9 

•655 106 19 16 

•656 107 2 22 

•657 107 6 4 

•658 107 9 11 

•059 107 12 17 

•660 107 10 0 

•661 107 19 6 

•602 108 2 12 

•663 108 5 19 

•664 108 9 1 

•665 108 12 8 

•666 108 15 14 

•667 108 18 20 

•668 109 2 3 

•669 109 5 9 

•670 109 8 16 

•671 109 11 22 

•672 ' 109 15 4 

•673 109 18 11 

•674 110 1 17 

•675 110 5 0 

•676 110 8 6 













ASSAY TABLE. 


xlii 


If 200 Grains of Ono Ton of Ore 
Ore give of will yield of 

FINE METAL FINE METAL 

Gr. 

•677 
•678 
•679 
•680 
•681 
•682 
•683 
•684 
•685 
•686 
•687 
•688 
•689 
•690 
•691 
•692 
•693 
•694 
•695 
•696 
•697 
•698 
•699 
•700 
•701 
•702 
•703 
•704 
•705 
•706 
•707 
•708 
•709 
•710 
•711 
•712 
•713 
•714 
•715 
•716 
•717 
•718 
•719 
•720 


If 200 Grains of One Ton of Ore 
Ore give of will yield of 

FINE METAL FINE METAL 


Gr. 

Oz. 

Dwts. 

Grs. 

721 

117 

15 

6 

722 

117 

18 

12 

723 

118 

1 

19 

724 

118 

5 

1 

725 

118 

8 

8 

726 

118 

11 

14 

727 

118 

14 

20 

728 

118 

18 

3 

729 

119 

1 

9 

730 

119 

4 

16 

731 

119 

7 

22 

732 

119 

11 

4 

733 

119 

14 

11 

734 

119 

17 

17 

735 

120 

1 

0 

730 

120 

4 

6 

737 

120 

7 

12 

738 

120 

10 

19 

739 

120 

14 

1 

740 

120 

17 

2 

741 

121 

0 

14 

742 

121 

3 

20 

743 

121 

7 

3 

744 

121 

10 

9 

745 

121 

13 

6 

740 

121 

16 

22 

747 

122 

0 

4 

748 

122 

3 

11 

749 

122 

6 

17 

750 

• 122 

10 

0 

751 

122 

13 

16 

752 

122 

16 

12 

753 

122 

19 

19 

754 

123 

3 

1 

755 

123 

6 

8 

756 

123 

9 

14 

757 

123 

12 

20 

758 

123 

16 

3 

759 

123 

19 

9 

760 

124 

2 

16 

761 

124 

5 

22 

762 

124 

9 

4 

763 

124 

12 

11 

764 

124 

* 15 

17 


Oz. Dwts. Grs. 


110 

11 

110 

14 

110 

18 

111 

1 

111 

4 

111 

7 

111 

11 

111 

14 

111 

17 

112 

0 

112 

4 

112 

7 

112 

10 

112 

14 

112 

17 

113 

0 

113 

3 

113 

7 

113 

10 

113 

13 

113 

16 

114 

0 

114 

3 

114 

6 

114 

9 

114 

13 

114 

16 

114 

19 

115 

3 

115 

6 

115 

9 

115 

12 

115 

16 

115 

19 

116 

2 

116 

5 

116 

9 

116 

12 

116 

15 

116 

'18 

117 

2 

117 

5 

117 

8 

117 

12 


12 

19 
1 

8 

14 

20 

3 
9 
6 

22 

4 
11 
17 

0 

6 

12 

19 
1 

8 

14 

20 

3 
9 

16 

22 

4 
12 
17 

0 

6 

12 

19 
1 

8 

14 

20 

3 
9 

16 

22 

4 
11 
17 

0 















ASSAY TABLE. 


xliii 


If 200 Grains of 

One Ton of Ore 

If 200 Grains of 

One Ton of Ore 

Ore give of 

will yield of 

Ore give of 

will yield of 

FINE METAL 

FINE METAL 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

Gr. 

Oz. 

Dwts. 

Grs. 

•705 

124 

19 

0 

•809 

132 

2 

17 

• 76 G 

125 

2 

6 

•810 

132 

6 

0 

•767 

125 

5 

12 

•811 

132 

9 

6 

•768 

125 

8 

19 

•812 

132 

12 

12 

•769 

125 

12 

1 

•813 

132 

15 

19 

•770 

125 

15 

8 

•814 

132 

19 

1 

•771 

125 

18 

14 

•815 

133 

2 

8 

•772 

126 

1 

20 

•816 

133 

5 

14 

•773 

126 

5 

3 

•817 

133 

8 

20 

•774 

126 

8 

9 

•818 

133 

12 

3 

•775 

126 

11 

16 

•819 

133 

15 

9 

•776 ‘ 

126 

14 

22 

•820 

133 

18 

16 

•777 

126 

18 

4 

•821 

134 

1 

22 

•778 

127 

1 

11 

•822 

134 

5 

4 

•779 

127 

. 4 

17 

•823 

134 

8 

11 

•780 

127 

8 

0 

•824 

134 

11 

17 

•781 

127 

11 

6 

•825 

134 

15 

0 

•782 

127 

14 

12 

•826 

134 

18 

6 

•783 

127 

17 

19 

•827 

135 

1 

12 

•784 

128 

1 

1 

•828 

135 

4 

19 

•785 

128 

4 

8 

•829 

135 

8 

1 

•786 

128 

7 

14 

•830 

135 

11 

8 

•787 

128 

10 

20 

•831 

135 

14 

14 

•788 

128 

14 

3 

•832 

135 

11 

8 

•789 

128 

17 

9 

•833 

136 

1 

3 

•790 

129 

0 

16 

•834 

136 

4 

9 

•791 

129 

3 

22 

•835 

136 

7 

16 

•792 

129 

7 

4 

•836 

136 

10 

22 

•793 

129 

10 

11 

•887 

136 

14 

4 

•794 

129 

13 

17 

•838 

136 

17 

11 

•795 

129 

17 

0 

•839 

137 

0 

17 

•796 

130 

0 

6 

•840 

137 

4 

0 

•797 

130 

3 

12 

•841 

137 

7 

6 

•798 

130 

6 

19 

•842 

137 

10 

12 

•799 

130 

10 

1 

•843 

137 

13 

19 

•800 

130 

13 

8 

•844 

137 

17 

1 

•801 

130 

16 

14 

•845 

138 

0 

8 

•802 

130 

19 

20 

•846 

138 

3 

14 

•803 

131 

3 

3 

•847 

138 

6 

20 

•804 

131 

6 

9 

•848 

138 

10 

3 

19 

•805 

131 

9 

16 

•849 

138 

13 

•806 

131 

12 

22 

•850 

138 

16 

16 

•807 

131 

16 

4 

•851 

138 

19 

22 

•808 

131 

19 

11 

•852 

139 

3 

4 


f 2 












xliv 


ASSAY TABLE. 


If 200 Grains of 

One Ton of Ore 

If 200 Grains of 

One Ton of Ore 

Ore give of 

will yield of 

Ore give of 

will yield of 

FINE METAL 

FINE METAL 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

Gr. 

Oz. 

Dwts. 

Grs. 

•853 

139 

6 

11 

•897 

146 

10 

4 

•854 

139 

9 

17 

•898 

146 

13 

11 

•855 

139 

13 

0 

•899 

146 

16 

17 

•856 

139 

16 

6 

•900 

147 

0 

0 

•857 

139 

19 

12 

•901 

147 

3 

6 

•858 

140 

2 

19 

•902 

147 

6 

12 

•859 

140 

6 

1 

•903 

147 

9 

19 

•860 

140 

9 

8 

•904 

147 

13 

1 

•861 

140 

12 

14 

•905 

147 

16 

8 

•862 

140 

15 

20 

•906 

147 

19 

14 

•863 

140 

19 

3 

•907 

148 

2 

2 

•864 

141 

2 

9 

•908 

148 

6 

3 

•865 

•866 

141 

5 

16 

•909 

148 

9 

9 

141 

8 

22 

•910 

148 

12 

16 

•867 

141 

12 

4 

•911 

148 

15 

21 

•868 

141 

15 

11 

•912 

148 

19 

4 

•869 

141 

18 

17 

•913 

149 

2 

11 

•870 

142 

2 

0 

•914 

149 

5 

17 

•871 

142 

5 

6 

•915 

149 

9 

0 

•872 

142 

8 

12 

•916 

149 

12 

6 

•873 

142 

11 

19 

•917 

149 

15 

12 

•874 

142 

15 

1 

•918 

149 

18 

19 

•875 

142 

18 

8 

•919 

150 

2 

1 

•876 

143 

1 

14 

•920 

150 

5 

8 

•877 

143 

4 

20 

•921 

150 

8 

14 

•878 

143 

8 

3 

•922 

150 

11 

20 

•879 

143 

11 

9 

•923 

150 

15 

3 

•880 

143 

14 

16 

•924 

150 

18 

9 

•881 

143 

17 

22 

•925 

151 

1 

16 

•882 

144 

1 

4 

•926 

151 

4 

22 

•883 

144 

4 

11 

•927 

151 

8 

4 

•884 

144 

7 

17 

•928 

151 

11 

11 

•885 

144 

11 

0 

•929 

151 

14 

17 

•886 

144 

14 

6 

•930 

151 

18 

0 

•887 

144 

17 

12 

•931 

152 

1 

6 

•888 

145 

0 

19 

•932 

152 

4 

12 

•889 

145 

4 

1 

•933 

152 

7 

19 

•890 

145 

7 

8 

•934 

152 

11 

1 

•891 

145 

10 

14 

•935 

152 

14 

8 

•892 

145 

13 

20 

•936 

152 

17 

14 

•893 

145 

17 

3 

•937 

153 

0 

20 

•894 

146 

0 

9 

•938 

153 

4 

3 

•895 

146 

3 

16 

•939 

153 

7 

9 

•896 

146 

6 

22 

•940 

153 

10 

16 













ASSAY TABLE. 


xlv 


If 200 Grains of One Ton of Ore 

Ore give of will yield of 

FINE METAL FINE METAL 

Gr. Oz. Dwts. Grs. 

•941 153 13 22 

•942 153 17 4 

•943 154 0 11 

•944 154 3 17 

•945 154 7 0 

•946 154 10 6 

•947 154 13 12 

•948 154 16 19 

•949 155 0 1 

•950 155 3 8 

•951 155 6 14 

•952 155 9 20 

•953 155 13 3 

•954 155 16 9 

•955 155 19 16 

•956 156 2 22 

•957 156 6 4 

•958 156 9 11 

•959 156 12 17 

•960 156 16 0 

•961 156 19 6 

•962 157 2 12 

•963 157 5 19 

•964 157 9 1 

•965 157 12 8 

•966 157 15 14 

•967 157 18 20 

•968 158 2 3 

•969 158 5 9 

•970 158 8 16 

•971 158 11 22 

•972 158 15 4 

•973 158 18 11 

•974 159 1 17 

•975 159 5 0 

•976 159 8 6 

•977 159 11 12 

•978 159 14 19 

•979 159 18 1 

•980 160 1 8 

•981 160 4 14 

•982 160 7 20 

•983 160 10 3 

•984 160 14 9 


If 200 Grains of One Ton of Ore 

Ore give of 

will yield of 

FINE METAL 

FINE METAL 

Gr. 

Oz. 

Dwts. 

Grs. 

•985 

160 

17 

6 

•986 

161 

0 

22 

•987 

161 

4 

4 

•988 

161 

7 

11 

•989 

161 

10 

17 

•990 

161 

14 

0 

•991 

161 

17 

6 

•992 

162 

0 

12 

•993 

162 

3 

19 

•994 

162 

7 

1 

•995 

162 

10 

8 

•996 

162 

13 

14 

•997 

162 

16 

20 

•998 

163 

0 

3 

•999 

163 

3 

9 

1 grain 

163 

6 

16 

2 

326 

13 

8 

3 

490 

0 

0 

4 

653 

6 

16 

5 

816 

13 

8 

6 

980 

0 

0 

7 

1143 

6 

16 

8 

1306 

13 

8 

9 

1470 

0 

0 

10 

1633 

6 

16 

11 

1796 

13 

8 

12 

1960 

0 

0 

13 

2123 

6 

16 

14 

2286 

13 

8 

15 

2450 

0 

0 

16 

2613 

6 

16 

17 

2776 

13 

8 

18 

2940 

0 

0 

19 

3103 

6 

16 

20 

3266 

13 

8 

21 

3430 

0 

0 

22 

3593 

6 

16 

23 

3756 

13 

8 

24 

3920 

0 

0 

25 

4083 

6 

16 

26 

4246 

13 

8 

27 

4410 

0 

0 

28 

4573 

6 

16 

29 

4736 

13 

8 














xlvi 


ASSAY TABLE. 


If 200 Grains of One Ton of Ore 

If 200 Grains of One Ton of Oro 

Ore give 

of will yield of 

Ore give 

of will 

yield of 

FINE METAL FINE METAL 

FINE METAL FINE METAL 

Grs. 

Oz. 

Dwts. 

Grs. 

Grs. 

Oz. Dwts. 

Grs. 

30 

4900 

0 

0 

74 

12086 

13 

8 

31 

5063 

6 

16 

75 

12250 

0 < 

0 

32 

5226 

13 

8 

76 

12413 

6 

16 

33 

5390 

0 

0 

77 

12576 

13 

8 

34 

5553 

6 

16 

78 

12740 

0 

0 

35 

5716 

13 

8 

79 

12903 

6 

16 

36 

5880 

0 

0 

80 

13066 

13 

8 

37 

6043 

6 

16 

81 

13230 

0 

0 

38 

6206 

13 

8 

82 

13393 

6 

16 

39 

6370 

0 

0 

83 

13556 

13 

8 

40 

6533 

6 

16 

84 

13720 

0 

0 

41 

6696 

13 

8 

85 

13883 

6 

16 

42 

6860 

0 

0 

86 

14046 

13 

8 

43 

7023 

6 

16 

87 

14210 

0 

0 

44 

7186 

13 

8 

88 

14373 

6 

16 

45 

7350 

0 

0 

89 

14536 

13 

8 

46 

7513 

6 

16 

90 

14700 

0 

0 

47 

7676 

13 

8 

91 

14863 

6 

16 

48 

7840 

0 

0 

92 

15026 ' 

13 

8 

49 

8003 

6 

16 

93 

15190 

0 

0 

50 

8166 

13 

8 

94 

15353 

6 

16 

51 

8330 

0 

0 

95 

15516 

13 

8 

52 

8493 

6 

16 

96 

15680 

0 

0 

53 

8656 

13 

8 

97 

15843 

6 

16 

54 

8820 

0 

0 

98 

16006 

13 

8 

55 

8983 

6 

16 

99 

16170 

0 

0 

56 

9146 

13 

8 

100 

16333 

6 

16 

57 

9310 

0 

0 

101 

16496 

13 

8 

58 

9473 

6 

16 

102 

16660 

0 

0 

59 

9636 

13 

8 

103 

16823 

6 

16 

60 

9800 

0 

0 

104 

16986 

13 

8 

61 

9963 

6 

16 

105 

17150 

0 

0 

62 

10126 

13 

8 

106 

17313 

6 

16 

63 

10290 

0 

0 

107 

17476 

13 

8 

64 

10453 

6 

16 

108 

17640 

0 

0 

65 

10616 

13 

8 

109 

17803 

6 

16 

66 

10780 

0 

0 

110 

17966 

13 

8 

67 

10943 

6 

16 

111 

18130 

0 

0 

68 

11106 

13 

8 

112 

18293 

6 

16 

69 

11270 

0 

0 

113 

18456 

13 

8 

70 

11433 

6 

16 

114 

18620 

0 

0 

71 

11596 

13 

8 

115 

18783 

6 

16 

72 

11760 

0 

0 

116 

18946 

13 

8 

73 

11923 

6 

16 

117 

19110 

0 

0 











ASSAY TABLE. 


xlvii 


If 200 Grains of One Ton of Ore 
Ore give of will yield of 

FINE METAL FINE METAL 


Grs.. 

Oz. 

Dwts. 

Grs. 

118 

19273 

6 

16 

119 

19436 

13 

8 

120 

19600 

0 

0 

121 

19763 

6 

16 

122 

19926 

13 

8 

123 

20090 

0 

0 

124 

20253 

6 

16 

125 

20416 

13 

8 

126 

20580 

0 

0 

127 

20743 

6 

16 

128 

20906 

13 

8 

129 

21070 

0 

0 

130 

21233 

6 

16 

131 

21396 

13 

8 

132 

21560 

0 

0 

133 

21723 

6 

16 

134 

21886 

13 

8 

135 

22050 

0 

0 

136 

22213 

6 

16 

137 

22376 

13 

8 

138 

22540 

0 

0 

139 

22703 

6 

16 

140 

22866 

13 

8 

141 

23030 

0 

0 

142 

23193 

6 

16 

143 

23356 

13 

8 

144 

23520 

0 

0 

145 

23683 

6 

16 

146 

23846 

13 

8 

147 

24010 

0 

0 

148 

24173 

6 

16 

149 

24336 

13 

8 

150 

24500 

0 

0 

151 

24663 

6 

16 

152 

24826 

13 

8 

153 

24990 

0 

0 

154 

25153 

6 

16 

155 

25316 

13 

8 

156 

25480 

0 

0 

157 

25643 

6 

16 

158 

25806 

13 

8 

159 

25970 

0 

0 


If 200 Grains of One Ton of Ore 
Ore give of will yield of 

FINE METAL FINE METAL 


Grs. 

Oz. 

Dwts. 

Grs, 

160 

26133 

6 

16 

161 

26296 

13 

8 

162 

26460 

0 

0 

163 

26623 

6 

16 

164 

26786 

13 

8 

165 

26950 

0 

0 

166 

27113 

6 

16 

167 

27276 

13 

8 

168 

27440 

0 

0 

169 

27603 

6 

16 

170 

27766 

13 

8 

171 

27930 

0 

0 

172 

28093 

6 

16 

173 

28256 

13 

8 

174 

28420 

0 

0 

175 

28583 

6 

16 

176 

28746 

13 

8 

177 

28910 

0 

0 

178 

29073 

6 

16 

179 

29236 

13 

8 

180 

29400 

0 

0 

181 

29563 

6 

16 

182 

29726 

13 

8 

183 

29890 

0 

0 

184 

30053 

6 

16 

185 

30216 

13 

8 

186 

30380 

0 

0 

187 

30543 

6 

16 

188 

30706 

13 

8 

189 

30870 

0 

0 

190 

31033 

6 

16 

191 

31196 

13 

8 

192 

31360 

0 

0 

193 

31523 

6 

16 

194 

31686 

13 

8 

195 

31850 

0 

0 

196 

32013 

6 

16 

197 

32176 

13 

8 

198 

32340 

0 

0 

199 

32503 

6 

16 

200 

32666 

13 

8 

























































































. 




























I N I) E X. 




ACID 

CID, acetic, 205 
— boracic, 218 
-action of the blowpipe on, 236 

— hydrochloric, 205 

— molybdic, action of tho blowpipe on, 
230 

— nitric, 205 

— nitro-hydrochloric, 205 

— oxalic, 158 

— sulphindigotic, 210 

— sulphuric, 206 

— sulphurous, 210 

— tartaric, 158 

— tungstic, action of the blowpipe on, 
230 

Adularite, 227 

Agents, desulphurising, 174 

— oxidising, 160 

— reducing, 154 
Agitator, 553 
Albite, 227 
Alcohol, 205 

Alkalies, action of, on sulphide of lead, 
374 

— caustic, 173, 180 

Alkaline carbonate, action of, on sulphide 
of lead, 374 

Alkaline persulphides, 182 
Allophane, 227 

Alloys, of copper and silver, assay of 
492 

— of platinum and silver, assay of, 492 
-silver and copper, assay of, 493 

— unknown, approximate determination 
of tho standard of, 550 

Alumina, action of the blowpipe on, 229 

— silicate of, 185 

— uses of, 185 

Amalgam, action of the blowpipe on, 577 
Amalgamation, process of, in an assay of 
silver, 480 
Amblygonite, 227 
Amethyst, violet, 693 
Ammonia, carbonate, 206 

— liquid, 206 

— oxalate of, 208, 159 
Ammonium, chloride of, 205 

— sulphide of, 206 
Amphibolite, 227 


AZU 

Analysis, volumetric, 238 

-standard solutions used in, 245 

-instruments and apparatus used in, 

246 

Anorthite, 227 
Antophyllite, 227 
Anthracite, 155 

Antimonial substances, classification of, 
427 

Antimonic acid, 427 

-action of blowpipe on, 436 

Antimonious acid, 427 

-action of blowpipe on, 435 

Antimony and its oxides, action of blow¬ 
pipe on, 437 

— action of oxide of lead on, 162 

— action of the blowpipe on, 435 

— assay of, 427 

-Mr. Sutton’s methods, 435 

— native, 427 

— ores of tho first class, assay of, 427 

-second-428 

— oxide of, 427 

— oxysulphide of, 417 

— regulus of, determination of, 429 
Antimony, sidphide of, 182, 427 
-(antimonium crudum) determi¬ 
nation of, 428 

Anvil, 11 

— stand, 11 
Apatite, 227 

Apparatus, auxiliary, to furnace opera¬ 
tions, 64 

-to tho blowpipe, 202 

Aqua marine, green, 694 
Argol, cream of tartar, or bitartrate of 
potash, 191 

— reducing power of, assay of, 468 
Arseniate of nickel, 662 
Arsenic, assay of, 651 

— native, 651 

— kies, 651 

— sulphides of, 651 

Arsenical pyrites, action of the blowpipe 
on, 293 

Arsenical kies, 651 
Automalite, 226 
Axinite, 227 
Azurite, 297 







1 


INDEX. 


DAL 

I BALANCE, assay, 23, 24 

)-theory of tho, 25 

Barium, chloride of, 206 
Baryta, 228 
— carbonato of, 228 
— nitrate of, 206 
— sulphate of, 227 
Beryl, 227 
— blue, 691 

Binary compounds, containing no oxygen, 
5 

Bismuth, action of the blowpipe on, 644 
— action of oxido of load on, 163 
— assay of, 641 

— assay of, in the wet way, 642 

-Balard’s method, 

642 

-by weight and by volume, Pear¬ 
son’s procoss, 643 
— cupriferous sulphido of, 641 
— distinguishing it from antimony and 
tellurium, 614 
— native, 641 

-assay of, 641 

-action of the blowpipe on, 644 

-determination of amount of, in the 

wet way, 642 
— oxide of, 641 

-action of the blowpipe on, 644 

— persulphide of, 641 
— plumbo-argentiferous sulphido of, 641 

-cupriferous sulphido of, 641 

— residues, cupel bottoms, 641 
— sulphido of, 641 

-action of blowpipe on, 644 

Blaekband, 252 
Bladders, 110 
Blowpipe, 196 
— and its use, 195 

— general routine of operations, 200, 224 
— auxiliary apparatus, &c. 202 
Bone ash, 219 
Boracite, 227 

Borax, biborate of soda, 185, 214 
Botryolite, 227 
Bournonite, 297 
Braunite, 653 
Brightening silvor, 480 
Bromides, action of the blowpipe on, 233 
Bullion, silver, assay of in the wet way, 
494 

Burette, 246 


nALAlTE, 227 
VJ Calamine, 437 
Calcination, 38 
Calcium, chloride of, 207 

— fluoride of, 187, 218 
Calorimeter, Ure’s, 145 

— Wri gilt’s, 146 
Caoutchouc, 110 
Carbon, 155 


COl’ 

Celestino, 227 
Cement, 107 

— Beale’s, 113 

— boiler, 113 

— Bruyore’s, 113 

— iron, 112 

— oxychloride of zinc, 113 

— resinous or hard, 110 

— Itoman, 108 

— soft, 108 

— waterproof, 109 
Cerite, 226 
Ceruse, 161, 193 
Charcoal, 155, 174 
Chalcopyrite, 297 
Chemical nomenclature, 1 
Chemical symbols, 3, 7 
Chisel, cold, 13 

Chlorides, action of the blowpipo on, 233 
Chlorine, 210, 235 
Chondrodite, 227 
Chrome ore, assay of, 646 

-determination of chromium by 

means of standard solution, 649 

— ochre, action of tho blowpipe on, 650 
Chromium, oxide of, action of tho blow¬ 
pipe on, 650 

Chrysoprase, green, 694 
Cinnabar, 182, 453 

—- in an ore, assay for the amount of, 
456 

— sulphide of mercury, action of the 
blowpipe on, 460 

Cinnamon stone, 688 

Cobalt, arseniate of, action of the blow¬ 
pipe on, 667 

— arsenical, action of tho blowpipe on, 
667 

— arsenio-sulphide of, 662 

— arsenites of, 662 

— assay of, 662 

— glance, action of the blowpipe on, 667 

— nitrate of, 218 

— ores, action of the blowpipe on, 666 

— oxide of, action of the blowpipe on, 
667 

-composition of, 662 

— sulphate of, 662 

— sulphide of, 662 

-action of the blowpipe on, 666 

Coke, 155 
Copper, 209 

— action of oxide of lead on, 165 

— argentiferous sulphide of, action of 
the blowpipe on, 369 

— arseniate of, 297 

-action of the blowpipo on, 370 

— assays, classification of, 298 

— assay, by precipitation with metallic 
zinc, 341 

-colorimetric, 342 

-Heine’s, 343 

-Jacquelin’s and Hubert’s, 350 







INDEX. 


li 


COP 

Copper assay, colorimetric, Muller’s, 354 

-English, 299 

-German, 319 

-in the dry way, 299 

-in the wet way, 336 

— — Kerl’s modified Swedish, 336 
-Levol’s method,-365 

— — Robert’s and Byer’s method, 365 
-Rivot’s method, 365 

-Wolcott Gibbs’ method, 367 

-volumetric, 365 

-Brown’s method, 362 

-Fleck’s modification of Mohr’s 

method, 363 

-Floitmann’s method, 364 

-Kunsel’s method, 357 

-Parkes’ and Mohr’s method, 359 

-Polouze’s process, 355 

-Schwarz’s method, 361 

— blowpipo, reactions of, 369 

— carbonate of, action of the blowpipe 
on, 370 

— chloride of, action of the blowpipo on, 
370 

— glance, 297 

— ores, classification of, 297 

— ores, sulphuretted, 297 
-oxidised, 297 

-of the first class, assay of, 299 

-second class, assay of, 333 

— oxides of, 165, 173, 194, 218 

-action of the blowpipo on, 370 

-action of oxide of lead on, 164 

— phosphate of, 297 

— pyrites, 297 

-action of the blowpipe on, 369 

_ red, 297 

— refining, 325 

— regulus, 297 

— speiss, 297 

— sulphate of, 174, 210 

— sulphide of, action of the blowpipe on, 
369 

-and of antimony, Bournonito, 

action of the blowpipe on, 369 

-and of tin, tin-pyrites, action of 

the blowpipe on, 370 
Corundum, 226 
Coruscation of silver, 480 
Covelline, 297 
Cream of tartar, 191 
Crucibles, 113 

— alumina, 122 

— charcoal, 118 

— lime, 121 

-- malleable iron, 123 

— platinum, 123 
Crysolite, 694 
Cupellation, silver, 478 
Cupels, 113, 128 
Cyanito, 226, 690 
Cyanosite, 297 
Cymophanc, 682, 696 


FUR 

ATHOLITE, 227 

Decime solution of common salt, 
preparation of, 498 
Decantation (elutriation), 18 
Desulphurising reagents, 174 
Diamond, 676 
Dichroite, 227, 691 
Disthene, 226, 690 
Distillation, 46 

Distilling assay (sulphur), 671 
Domoykite, 297 
Dressing, 19 


E LAOLITE, 227 

Eloctrum, action of the blowpipe on, 
5 77 

Elutriation, 18 
Emerald, 227 

— antique, possessing a play of colours, 
696 

— green, 694 
— yellow, 684 
Epidote, 227 
Erubescitc, 227 
Essonite, 688 
Ether, 205 
Euclaso, 227 
Eudyalite, 227 

TAAHLERZ, 297 
Jl Felspar, 696 
Ferrocyanide of potassium, 208 
Ferridcyanide of potassium, 208 
Flames, coloured, 234 
Fluor spar, 187, 218, 227 
Fluorides, action of the blowpipe on, 233 
Fluxes, 183, 194 
— black, white, and raw, 189 
— comparative reducing power of, 192 
— for smelting iron ores, analysis of, 267 
— metallic, 193 

— and reagents for the blowpipe, 205 
Franklinite, 437 

Fuol, absolute heating power of, 141 
— ash of, 150 

— assay and analysis of, 138 
— different peculiarities of, 152 
— external appearance of, 139 
— its adhering water, 140 
— pyrometric heating power of, 148 
— specific gravity of, 140 
— specific heating power of, 148 
— sulphur contained in, 151 
— volatile products of, 149 
Fulguration of silver, 480 
Furnaces, 52 

— auxiliary apparatus, 64 
— blast, 57 
— calcining, 52 

— effects produced by wind and blast, 69 
— evaporating, 54 






INDEX. 


lii 

FUR 

Furnace fusion, 54 

— gas, or gas blast, 77 

-arranged for heating at the top, 80 

-examples of fusion affected by, 86 

-Gore’s, 91 

-heated at the bottom, 84 

-miscellaneous use of, 89 

— — precautions to be observed, on com¬ 
mencing a fusion, 83 

-process of fusion in, 82 

-reverberatory, Griffin’s, 96 

-repair of, 89 

— method of measuring the heat of, 113 

— muffle or cupel, 59 

— oil, 71 

— •— description of the apparatus, 71 

-lamp, blowing power required, 76 

-management of, 73 

-power of, 76 

-operations, 63 

— wind, 54 
Fusion, 44 


p ADOLINITE, 227 
vT Gahnite, aluminate of zinc, 226 
Galena, 182, 373 
Garnet, deep red, 689 

— noble, 689 

— possessing a play of colours, 696 
Gases, examination of, 49 

-correction for moisture, 50 

-pressure, 50 

-temperature, 49 

Gems, discrimination of, 674 
Gehlinite, 226 

Glass, 185 

— analyses of, 186 

Gold, action of the blowpipe on, 623 

— alloyed with silver, parting of, 612 

— alloys, general observations on the 
assay of, 606 

-gold and copper, proportion of lead, 

607 

-table for the proportion 

of lead to be employed with cupellation, 
610 

-gold and lead, cupellation, 606 

-proof of the touchstone, 608 

-standard of, 618 

— artificial alloys of, 606 

— assay of substances of the first class, 602 

— assay of, weights for, 31 

— graphic, action of the blowpipe on, 623 

— native, composition of several va¬ 
rieties of, 600, 602 

— and palladium, composition of, 606 

— perchloride of, 209 

— plumbo-argentiferous, 606 

— and rhodium, 605 

— silver and copper, assay of the alloys 
of, 618 


IRON 

Gold, silver, platinum, and copper, assay 
of, 610 

— sulpho-plumbiferous, 606 

— telluride of, argentiferous, 606 
-and other mineralised sub¬ 
stances containing gold, assay of, 623 

— telluriforous and plumbiferous, action 
of the blowpipe on, 623 

Graphite, or black lead, 155 
Gum, 158 

Gypsum, sulphate of lime, 218, 227 

H AIDINGERITE, 427 
Hammers, 12 
Haematite, brown, 251 
— red, 251 
Hausmanite, 653 
Hauyn, 227 
Horn mercury, 460 
Hydrochloric acid, 205 
Hydrogen gas, 154 
— sulphuretted, 206 

TDOCRASE, 227 

X Iodides, action of the blowpipe on, 
233 

Iron, 174 

— action of oxide of lead on, 164 
— assay of, 251 

-in the dry way, 252 

-in the w r et way, 268 

-Fuchs’s method, 268 

-Marguerite’s me¬ 
thod, 269 

-Mr. Blunt’s 

observations on, 274 

-Mittenzwey’s pro¬ 
cess, 281 

-Dr. Penny’s process, 

275 

-Titration of iron by 

protochloride of tin, 282 
— carbonate of, spathose ore, 251 

-action of the blowpipe on, 294 

— chromate of, action of the blowpipe 
on,293 

— ores, analysis of, 267 
— ore, argillaceous, 251 

-assay of, by Professor Abel, 259 

— — blowpipe reactions of, 293 
-magnetic, 251 

— — quantitative determination of all 
the constituents usually present in, 
286 * 

— oxide of, 174, 194 

-action of the blowpipe on, 294 

hydrated, action of the blowpipe 
on, 294 

— peroxide of, 174 

-action of oxido of lead on, 164 

— protoxide of, distinguishing it from 
sesquioxide, 295 













IRON 


INDEX. 


liii 


Iron pyrites, 182 

-action of tho blowpipe on, 293 

-magnetic, action of the blowpipe 

on, 293 

— red siliceous, 252 

— samples, analysis of, 263 

— sesquioxide of, 207 

— sulphate of, 174, 210 

K OBOLDINE, 662 
Kupfernickel, 662 

L ABBADOBITE, 227 

Laws of combination, 5 • 
Lazurstein, 227 

Lead, action of the blowpipe on, 236 
— assay of, 373 

-additional remarks on, 395 

-—-by roasting and reducing, 387 

-fusion with black flux, 382 

-carbonate of potash, 375 

-carbonate of soda, or with 

black flux and metallic iron, 385 

-metallic iron, 383 

-— Levol’s fusion with ferrocyanide 

and cyanide of potassium, 397 

-Markus’ experiments on, 395 

-Schemnitz, 397 

•-substances of the first class, 

373 

-in the wet way, 

388 

-fourth class, alloys, 

395 

-second class, 390 

-in the wet way, 

393 

--third class, 393 

-in the wet way, 

394 

— assay, volumotric, Flores DumontAs 
method, 397 

-Hempel’s method, modified, 401 

-Schwarz’s method, 398 

-of, with sulphuric acid, 388 

— blowpipe reactions of, 405 
— borate of, 166, 193 
— carbonate of, action of the blowpipe 
on, 406 

— classification of tho substances con¬ 
taining lead, 373 

— determination of, by means of stan¬ 
dard solutions, 397 

-by oxalic acid, 405 

-in the state of carbonate, 404 

— glass of, silicate of lead, 193 
— neutral acetate of, 210 
— nitrate of, 173, 181 
— oxide of, action of the blowpipe on, 
406 

— phosphate of, action of the blowpipe 
on, 406 


MER 

Lead, proof, 219 

— silicate of, 166 

— sulphate of, 174, 181, 193 
-action of the blowpipe on, 406 

— sulphide of (galena), action of the 
blowpipe on, 406 

-action of alkalies and alkaline 

carbonates on, 374 

— --argol on, 374 

-metallic iron on, 373 

-nitrate of potash on, 374 

-oxygen on, 373 

— white, mixed with oil, 108 

-ceruse, 161, 193 

Leucite, 226 

Lime, 185 

— action of the blowpipe on, 229 

— silicate of, 185 

— sulphate of, 209 

— tungstate of, 227 

— water, 209 

Litharge, 125, 160, 174, 193 

— assay of, for silver, 468 
Lithia, 228 

Lutes, 107 

— fat, 108 

— lime and egg, 108 


M alachite, 297 

Magnesia, 185 

—• action of the blowpipe on, 229 
— silicate of, 185 
— sulphate of, 209 
Magnesium, chloride of, 210 
Magnetic iron ore, 251 
— pyrites, 293 

Manganese ores, assay of, 653 

-Fresenius and Will’s method, 

656 

— oxide of, action of the blowpipe on, 660 
— peroxide of, 173 

-action of the blowpipe on, 660 

— sulphide of, action of the blowpipe on, 
660 

Manganite, 653 
Meal, linseed or almond, 108 
Measuring flasks, 249 
Meerschaum, 227 
Meionite, 227 

Mercurial ores, assay of, 453 

-for amount of cinnabar in, 456 

Mercury, action of the blowpipe on, -160 
— assay of, 453 
— chloride of, 210 

-action of the blowpipe on, 460 

— iodide of, 453 
— native, 453 
— oxide of, 210 
— selenido of, 453 
— subchloride of, 453 
— subnitrate of, 210 










liv 


INDEX. 


MER 

Mercury, subsulphide of, zinciferous, 453 

— sulphide of, bituminous, 453 
-zinciferous, 453 

-cinnabar, action of the blowpipe 

on, 4G0 

— volumetric estimation of, 456 
Minium, action of the blowpipe on, 406 
Mispickol, action of the blow r pipe on, 293 


N EEDLE ORE, action of the blowpipe 
on, 370 

Nepheline, 227 

Nickel, action of the blow 7 pipe on, 668 
— antimonio-sulphide of, 662 
— arseniate of, 662 

— arsenical, action of the blowpipe on, 
668 

— arsenide of, 662 

— arsonio-sulphide of, grey nickel, 662 
— arsenite of, 662 
— ores, 662 
— oxalate of, 218 
— oxide of, 662 

-action of the blow T pipe on, 668 

— Plattner’s blowpipe assay, 669 
— separating from cobalt, 664 
— silicate of, 662 
— sulphide of, 662 

-action of the blowpipo on, 668 

Nitrates, action of the blow'pipe on, 233 
Nitre, nitrate of potash, 166, 181 
Nitrous vapours, moans of protection 
from, disengaged from the bottles 
during the assay in the wet way, 563 
Nomenclature, chemical, 1 
Normal solution of common salt, appa¬ 
ratus for filling the pipette by aspira¬ 
tion, and for convenient adjustment, 
560 

-preserving at a con¬ 
stant temperature, 562 

--apparatus for weighing, 

559 

-correction of the standard, 

when the temperature varies, 520 
-graduation of, the tempe¬ 
rature being different to that at which 
it is wished to be graduated, 549 

-methods of measurement 

in the employment of volumes instead 
of weights, 509 

-preparation of, measuring 

by volumes, 517 

-whon measured by 

weights, 501 

-preservation of, 505 

-in metallic vessels, 

515 

-table of corrections for 

variations in temperature, 522 
-temperature of, 514 


PUL 

Normal standard solution of iodide of po¬ 
tassium, 458 

—•-bichloride of mercury, 458 

Nosin, 227 


O IL, fat, 157 

Oligoclase, 227 
Olivine, 227 
Orpiment, 651 
Orthite, 227 

Oxidation by the use of the blowpipe, 
202 

Oxide, 4 

Oxides, metallic, reduction of, 212 
Oxidising agents, 160 
Oxygen, 160, 174 


P ALLADIUM and gold, 606 
Paper, 110 
— Brazil wood, 206 
— litmus, 206 
—- soda, 224 
— turmeric, 206 
Paris, plaster of, 108 
Peridote, chrysolite, 694 
Pestle and mortar, iron, 13 
— -— — porcelain, 13 

-steel, 16 

Petalite, 227 

Phosphates, action of the blowpipo on, 
234 

Phosphoric acid, action of the blowpipe 
on, 237 
Pipette, 249 

Platiniferous residues, extraction of metals 
from, 637 

Platinum, assay of, 624 
— bichloride of, 209 
— ores, analysis of, 624, 633 

-treatment of tho alcoholic solution 

of, 630 

— as a support before tho blowpipe, 204 
Pleonasee, 226 
Potash, acetate of, 209 
— action of the blowpipo on, 228 
— bisulphate of, 217 
— carbonate of, 187, 228 
— caustic, 206 
— chromate of, 207 
— nitrate of, 166, 181 

-oxidising power of, assay of, 468 

— sulphate of, 207 
Potassium, cyanide of, 207 
•— ferrocyanide of, 208 
— ferrideyanide of, 208 
— sulphocyanido of, 208 
Precious stones, 674 

Preparation, mechanical, of minerals for 
assay, 9 

Psilomolan, 653 
Pulverisation, 10 















INDEX. 


lv 


PYR 

Pyrites, copper, 671 

— iron, 671 
Pyrolusite, 653 
Pyrometer, Bystrom’s, 134 

— Daniell’s, 131 

— thermo-electric, 136 

— Wedgwood’s, 131 

— Wilson’s, 134 
Pyrosmalite, 227 
Pyroxenes, 227 

UARTZ, 226 

— crystalline forms of, 677 

— possessing a play of colours, 696 

— violet, 693 

— yellow, 685 

I )EALGAR, 651 
l Reagents in the dry way, 210 
— in the wet way, 205 
Reducing powor of tho various fluxes, 159 
Reduction, 42 
— of metallic oxides, 212 
— by the use of the blowpipe, 202 
Refining copper, 325 
Resins, 157 

Rhodium and gold, 605 
Roasting, 40 
Ruby (spinel), 689 

S ALT, common, chloride of sodium, 188 

-decime solution of, 498 

-normal solution of, apparatus for 

filling the pipette by aspiration, etc. 560, 
561 

-apparatus for preserving 

at a constant temperature, 562 

-— apparatus for weighing, 

559 

-correction of the standard 

of when the temperature varies, 520 
-graduation of the tem¬ 
perature being different to that at 
which it is wished to be graduated, 549 

-measurement of, 496 

-method of weighing, 496, 

500 

-preparation of, when 

measured by weight, 501 

-preparation of, when 

measured by volume, 509 

--preservation of, 505 

-in metallic vessels, 

515 

--table for the assay by tho 

wet way of an alloy containing any 
proportion whatever of silver, by the 
employment of a constant measure of 
the, 522 

-table of correction for 

variations in temperature, 522 


SIL 

Salt common, normal solution of, tempera¬ 
ture of, 514 
Salts, 4 
Saltpetre, 166 

— assay of, 167 

-IIuss’s method, 167 

-Gay-Lussac’s method, 169 

Sapphire, blue, 690 

— green, 694 

— possessing a play of colours, 696 

— red, 689 

— violet, 693 

— water, 691 

— white, 679 

— yellow, 682 
Schwerstein, 227 
Scorification of silver, 470 
Scorifier, 130 

Selenium, action of tho blowpipe on, 232 
Selenides, action of the blowpipe on, 232 
Serpentine, 227 
Shears, 13 
Sieve, the, 17 

— extempore, 17 
Sifting, 17 
Silica, 184, 218 

— action of the blowpipe on, 231 
Silicates, action of tho blowpipe on, 23 4 
Silver, action of the blowpipe on, 576 

— alloys containing mercury, modifica¬ 
tions required in tho assay of, 558 

-of silver and copper, special in¬ 
struction for the assay, 491 

— alloy, standard of a, application of tho 
process described in the determination 
of, 507 

— amalgam, action of the blowpipo on, 
577 

— antimonial and argentiferous antimony, 
action of tho blowpipe on,. 576 

— assay of, pure or nearly puro, the tem¬ 
perature of the normal solution of salt 
being that at which it was standardised, 
546 

— aurides of, 603 

—■ blowpipe assay of, by David Forbes, 
577 

-reactions of, 576 

— bullion, assay of by tho wet way, 491 
-proper of, 491 

— chloride of, dry, 219 

-reaction of the blowpipo on, 577 

-reduction of, obtained in tho 

assay of alloys in the wet way, 556 

— commercial, assay of, 569 

— and copper, general remarks on tho 
assay of the alloys of, 487 

— — — special instructions for tho 
assay of alloys of, 491 

-special instructions for the assay 

of, assay for approximate quantity of 
alloy, 491 

— decime solution of, preparation of, 499 











INDEX. 


SIL 

Silver, electrum, action of the blowpipe 
on, 577 

— estimation of, in ores and alloys by 
iodide of starch, 5G7 

— glance, 461 

— ingot, method of taking the assay 
from, 564 

— ores, 461 

-brittle, 461 

-dark red, 461 

-and alloys, classification of, 461 

-of the first class assay of, 

general observations, 461 
-special instruc¬ 
tions, 466 

-admixed with me¬ 
tallic silver, assay of, 476 

-second class assay of, 487 

-fusion with oxidising reagents, 463 

-litharge, 463 

-light red, 651 

.— native, assay of, 493 

— nitrate of, 207 

— oxide of, action of the blowpipe on, 
577 

— pure, preparation of, 557 

— and platinum, assay of alloys of, 492 
-and copper, 493 

— process of amalgamation in an assay 
for, 486 

— rod, action of the blowpipe on, 576 

— separating from galena, 487 
Soap, white and mottled, 192 

Soda, ammonio-phosphates of, micro- 
cosmic salt, 215 

— carbonate of, 187 

-fusion of substances with, 210 

— nitrate of, 166, 181 

— phosphate of, 208 

— sulphate of, 228, 174 
Sodalite, 227 
Solution, 45 

Sorrel, salt of, 191 
Spathose iron, 251 
Spar, heavy, 227 

— tabular, 227 
Speckstein, 227 
Spinel, 226, 689 
Spodumene, 227 

— soda, 227 
Standard solutions, 245 
Starch, 158 

— paste, 210 
Staurolite, 227 
Stones, blue, 690 

— brown, and flame-coloured, 686 

— colourless, 676 

— possessing a play of colours, chatoyant, 
695 

— red and rose-coloured, 689 

— violet, 693 

— yellow, 682 

Strontia, action of the blowpipe on, 229 


VER 

Sulphur, 181 

— action of the blowpipe on, 231 

— assay for, by distillation, 671 

-in the wet way, 672 

Sulphurous earth, 671 

rpALC, 226 
J- Tallow, 157 
Tantalite, 227 

Telluride of gold, argentiferous, 603 

-plumbo-argentiferous, 603 

-sulpho-plumbiferous, 603 

— of silver, 487 

Tellurium, action of the blowpipe on, 
161 

— oxide of, action of the blowpipe on, 
236 

Tetartine, 227 

Tin, action of oxide of lead on, 163 

— assay of, 407 

— blowpipe reactions on, 425 

— ores, action of the blowpipe on, 425 

— ores, assay of, containing arsenic, sul¬ 
phur and tungsten, 413 

-containing silica and slags, 

412 

— oxide of, action of blowpipe on, -125 

— oxide of, assay of, admixed with 
silica, 411 

-concretionary, wood tin, 407 

-crystallised, 407 

-disseminated, 407 

— -estimation in the wet way, 415 

-by means of a 

standard solution, 417 

— oxide of, sandy, 407 

— protochloride of, 208 

— pyrites, action of the blowpipe on, 
425 

Tinfoil, 219 
Titaneisen, rutile, 227 
Titanite, 227 
Topaz, 227 

— blue, 691 

— reddish, 689 

— w r hite, 679 

— yellow, 683 
Tourmaline, 227 

— blue, 691 

— green, 694 

— red, 689 

— violet, 693 

— yellow, 683 
Trough, pneumatic, 49 
Tunaberg, 667 

Tungstic acid, action of the blowpipe on, 
230 

Turquoise, 227, 692 

T7ANNING, 19 
V Varvicite, 653 
Vermeil garnet, 686 








INDEX. 


lvii 


VER 

Vermeil garnet, noble garnet, almandine, 
686 

Vesuvian, 227 

W ASHING, 19 

Water, distilled, 205 
Wax, yellow, 108 
Weighing, 23, 32 
Weights, 30 

— comparative of blue stones in air and 
water, 692 

-brown and flame-coloured stones, 

ditto, 688 

-green stones, ditto, 695 

-red and rose-coloured stones, 

ditto, 690 

-stones possessing a play of 

colours, ditto, 697 

-violet stones, ditto, 686 

— gold assay, 31 
— silver assay, 31 
Wire, iron, 209 
Wolfram, 227 
Wolfsbergite, 297 

Z EYLANITE, 226 
Zinc, 209 

— action of oxide of lead on, 163 
— aluminate of, Gahnito, 437 
— anhydrous carbonate of, calamine, 
437 

— anhydrous silicate of, 437 
— assay, 437 

-volumetric, 444 

-Mohr’s method, 450 


ZIR 

Zinc, assay, volumetric, SchafFner’s method, 
modified by Kiintzel, 444 
-Schwarz method, 449 

— blende, black jack, sulphide of zinc, 
action of the blowpipe on, 451 

— blowpipe reactions of, 451 

— carbonate of, action of the blowpipe on 
451 

— determination of the amount of, in 
the wet way, in ores of the first class, 
441 

— hydrated carbonate of, 437 

— — silicate of, electric calamine, 437 

— ores of the first class, assay of, 437 

-second-442 

-- — third-442 

-fourth-444 

-humid determination of zinc in ores 

of the first class, 441 

-second 

class, 442 

-— —-—-third 

class, 443 

----fourth 

class, 444 

— oxide of, action of the blowpipe on, 
451 

-earthy, 437 

-manganiferous, 437 

— oxysulphide of, 437 

— selenide of, 437 

— sulphate of, 437 

— sulphide of, black jack, 437 
Zircon, hyacinth, 226, 686 

— white, 678 

— yellow, 682 


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